That DSS’s mum losing her house isn’t our problem.

Legally, your other half doesn't have to support his son through uni- my husband didn't. It isn't his responsibility to pay his ex's mortgage/rent either. Sorry if that sounds harsh.

I would say, not your problem. She should pick it up with the bank. Editing as I realised you say she is in rented accommodation. She should speak with her landlord. Sounds like she has mismanaged her finances and using you as the cash cow. It would be a flat no from me.

Absolutely not yours or your DH's problem. Time for DSS's mum to stand on her own two feet and either get a job with a proper income or sell up and live somewhere she can afford.

I’m presuming that The OP is the second wife and therefore she’s probably got no clue what the real settlement was. Or the reason why, she’s just got her new husband’s version of events.

Then @heavenknowneeds to come back and confirm, I’d taken it as the maintenance was supposed to go until the summer until a lump sum was negotiated in order to end the maintenance early. Why mention the lump sum for her business at all if the agreement was only ever until Christmas 25? (There’s no reason for this to have been the point maintenance ended, it usually ends at 18, or when child leaves school or when child finishes full time education, it was clearly a renegotiation to get the lump sum.)

That is not what the OP said. She stated "The agreement they had in place was financial support ended in Dec 25. (Due to lump sum payments requested by ex)"
People have invented the "until the end of full time education" narrative. Since the son is at university and is 20 yrs old, there are no legal obligations to pay in respect of child maintenance anyway. It could well be a divorce agreement but that doesn't give the Ex the right change the agreement with a month to go.

But generally, 50/50 means no maintenance, noting there are some exceptions

Sorry this isn’t true - 50/50 time does not mean you’ll never have to pay maintenance. The very fact this was agreed to go up until DSS leaves all forms of full time education, not just 18/school, suggests this was part of a divorce settlement.

If the son is taking a gap year and will be living in the house as opposed to going travelling or whatever, then it is reasonable (but not an ideal situation) that he should contribute as 20 year olds eat a lot and use a lot of energy and water. If he is taking a gap year to save for uni then it's a shame if he has to use money to contribute so perhaps his dad should be thinking about that. He also may not want to live with you full time if he feels loyalty towards his mother - I don't think my children would do that.
I'm interested to know how much you will be supporting him throughout uni or if he will be using his mum's address in order to gain maximum eligibility to student maintenance loans to avoid you having to pay as much.

Okay, so that isn’t true and it’s a myth that needs debunking just because the other parent has the child approximately 50-50 and it never is
Doesn’t mean to say that child Maintainence wouldn’t be owed

They have him 50% of the time so every penny they have given to her was out of generosity not necessity. So no, they don’t have any obligation to pay a penny more. She needs to sort her life out.

20 year olds should be contributing.

Again, the elephant In the room is how did she end up in rented accommodation after the divorce?
How actually did that happen?
Given the age of the child gives me a rough indication as to when they were married and when they started their lives together there should’ve been a property to split. Where is that? What happened? Give us some more detail surrounding the settlement. Never mind the bloody 50-50 split Maintainence.
What happened to the lump sum that your DH paid her?

I do think you and your DH need to take a big hard look at your own mistakes here. Maintenance is for keeping the child. Your DH agreed to maintenance that continued until DSS left full time education and DSS doesn’t leave full time education until the summer.

It is regularly said that maintenance should never be spent on the mother or other non-related children, but on housing and keeping the child it is for, yet your DH (and I assume you) agreed to give exW a lump sum knowing she wouldn’t be spending it on DSS/his support but on supporting her failing business. That was a terrible decision.

Your DH agreed to pay maintenance until education finished. He should stick to that commitment he made to his child, his stupid decision to give this lump sum for a failing company shouldn’t effect this as both understood that lump sum wasn’t for DSS maintenance.

(the only way a lump sum instead of regular maintenance would be acceptable would be if DSS had gone to a uni in a different city and the lump sum was to pay for rent/uni halls for the year instead of monthly amounts. Only if it was a lump sum to cover DSSs needs not his mothers)

She asked for the extra money to pay a large business debt,

There's no way I would have paid this! Fine to support your child through university but why would you/DH pay his ex's debts?! How much was it?

If she can't afford her rent, she needs to downsize or work more-it's not your responsibility.

It's an adoption term from America to refer to a woman who is the biological mother but has given up her parental rights and the child has an adoptive mother whom the child is brought up by, lives full time with etc. and in all respects other than biology the mother of the child.

Some step parents use "bio mum" to put the child's mother in her place, or because they genuinely don't understand, but it's misused in that context.

Well, shes not your responsibility but it has become a problem.for you. Maybe a discussion with DSS before you decide? Its hard to make financial suggestions without more detail, especially about her business and the timefrane, previous payments etc, but I'd say she has had plenty of notice that the money is going to stop. Your worry seems to be more about the pressure she'd put on DDS, so, as I said, talj to him if you can.

What a loser she sounds. Grifting off of everyone in sight. What is her line of "business," an MLM? If she needed a large lump sum loan it must not be profitable. Why can't she get out and get a job like everyone else?

We both feel the support needs to stop, or it never will I agree with you. It sounds like there will always be a big debt or a financial crisis looming.

She is in rented accommodation Then she either needs to find another job or move somewhere cheaper, even if it’s not as nice. She can’t ponce off her son indefinitely. Is he supposed to live with her and pay the rent forever? What happens if he wants to buy somewhere? Or he meets someone he wants to move in with? Who will pay her rent then? The situation is unsustainable.

Our fear is either this disrupts His last few months of uni, or she’ll in some way stop him going travelling so he can work to support him I’d say that’s a very realistic fear. In your shoes, I’d send DH up to see him to talk to him about it, reassure him that he’ll always have a home with you, but that his mum must downsize to somewhere she can afford by herself or DS will find himself trapped and responsible for her forever, and that your DH is really concerned that DSS will be guilt tripped into giving up his life. I’d stay out of it if I were you, just so there can be no suggestion of second wife wanting to see first wife out on her ear, and because DSS is not going to want to hear any criticism of his mum by anyone else.

But you had DSS 50:50 so legally no maintenance was due and your DH has been hugely generous already.

Big drip feed! In that case the mum would need to stay in the property till evicted so as to go on the council housing list, which could take months anyway. Sad for her and the DSS but not your financial responsibility.

Definitely time to walk away. DSS is an adult anyway now so he will surely be able to see how his Mum is manipulating things? You and DH have been way more generous than you needed to be.

He will have a home with you. She needs to fend for herself.

Do people actually say 'bio mum' in real life? it makes it seem like theres a variety of types of mums, there isn't. There's just the kids mum.

If she’s in so much financial difficulty that six to twelve months is going to be the difference between her keeping and losing the house, then I can’t see what difference it would make. What’s going to change in that time? Will she be knocking self employment on the head and getting a job with a wage high enough to pay the mortgage? Or is she thinking that her DS will be graduating in six months, he’ll be getting a job and then she can rely on him to pay the mortgage?

She appears to be living beyond her means and needs to downsize to a flat or somewhere where she can afford the monthly repayment. How many years have they been divorced? If it’s a good few years, then she doesn’t really have any excuse for not planning for this. If it’s only a year, and there she was thinking that keeping the house wouldn’t ever be something she’d need to worry about, then I’d have far more sympathy for her.

I think it very much depends on the circumstances. No, technically it’s not your problem. I’m presuming that the lump sums are what your DH would have paid for his share of putting him through uni? But it might be an idea to think very carefully about the practicalities of him graduating. Will he go to pieces if he’s worrying about his DM being homeless? Would you have him living with you until he gets a job? Or would you and your DH bypass DS’ mum and offer help with rent directly to your DSS until he’s got steady employment. And what sort of employment is he looking at here? Are we talking about him being offered prestigious graduate positions at high performing companies? Or is it more likely to be a job in the Co-op until he finds something? How long is support likely to be needed for? Will your DH let his DC suffer because of the poor financial planning of his mum?