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

Does DSS live at his mother’s home or is he away for uni? Does exW give the maintenance to DSS to live off /pay rent if he lives away and can’t afford to do that without help? (If so, would your DP give money directly to DSS)

DH has paid a generous maintenance throughout.

As well he should, he doesn't get bonus points for paying for his own child.

Why exactly is she in such trouble? If your husband pays maintenance then that must mean his son lives mainly with her and maintenance rarely covers the true cost of running a home large enough for the resident parent and any children? How independent is his son? And how will his life be impacted if his mother loses her home? Does she rent or is it a mortgage?

More details needed, really.

Agree with others - how will it affect DSS, does he live there? If she loses the house is he homeless too? In which case I think his father would have a moral obligation to house him - either by having him live with you or funding a place for him until he finds his feet post uni. Then there's how your DSS is likely to react to the idea that his dad has made his mum homeless - rightly or wrongly that could open a big can of worms.

You might conclude it's not worth the hassle for the sake of paying a few more months, but it depends.

Not your problem. How long is the entitlement going to go on for?! She can't be bankrolled forever on the basis of getting pregnant over 20 years ago

It’s not your problem.

how I would feel about it depends on the context. Personally I downsized after divorce.

A lot obviously depends on the financial situation of OPs DH too and how he would feel if the DSS and his mum had to move a long way away to find affordable housing.

And still not the OP’s problem

Why will she be able to stay in her house forever if your DH pays her for another six months? Has she got some big invoice that's going to be paid to her in this time and she has cashflow issues?

Otherwise she's leaving either now or in six months regardless.

It isn't your problem, no. But the lad needs somewhere to live. He can't be expected to just go out on his own in a bedsit or HMO straight out of uni when he may not even have a secure job. That kind of stuff was feasible about 25 years ago. But not now.

So if she has nowhere for him then you must put him up at yours. Of course he should pay board when he's working and cook, clean, do own laundry, pay for own phone etc. But not market rate rent.

@heavenknow Not your problem but as others voiced: how does your DSS feel about this or is he unaware?

Could you make it a loan and get her to sign to repay any monies you give her?

The difference is possibly that their child can not contribute at all for the next 6 months as he is still at uni. So by stopping in December it sounds like only one parent - the mother - will still be contributing for him and not the father at all.

And surprisingly hard to get.

Depends what “works for herself” means, is she a professional web designer, or is she selling crotcheted egg cosies on Etsy? Maybe she needs to think about getting a job which has a guaranteed income.

I had this when my ex stopped paying 5 months before Ur was due to end. With Jo court order there was basically nothing I could do and with our son just finishing uni and our daughter just starting it was bloody awful. It's a financial shock losing maintenance but you just have to get on with it. I got a second job.

This isn’t black and white as it depends how independent their child is. If he still needs help financially, as many 20 years olds do for whole hosts of reasons, then yes of course his father should still contribute.

She can downsize to a flat maybe?

No, I wouldn't do any of that 😂

She can get an evening job in bar and week ends for a year

Probably not going to touch the sides of a mortgage

Nah, you don’t have to do any of this, OP. Any stress to DSS has been caused his DM’s lack of planning; what is going to change in 6 months? It will just be the same plea again.

She can sell her home and downsize like everyone else who finds themselves in the position of not being able to pay for their home, and who doesn’t have a wealthy ex to emotionally blackmail for support.

She can get an evening job in bar and week ends for a year .

I would say, no, it’s not. It sounds like she needs to seek stable employment if her self employed work is not paying the bills.

But his dad should be (a) offering SS a place to live if she needs to downsize? and (b) sufficiently contributing to SS’s uni and living costs so that it’s not all falling on her.

It’s not your problem. But I do think you have a moral responsibility to house the 21year old if his mum can’t. Few 21 yr olds can afford to live along nowadays.

When did she know the agreement was ending early?
what were the lump sum payment for?

We don't know the mum's circumstances, life can be hard for single parents. I'm assuming you and DH are showing some compassion to her and to DSS. I think fwiw DSS should then have somewhere to come back to with you and DH. So presumably you have a room for him.

OP hasn't mentioned having a daughter? The parent of the adult is incapable of affording her house so will need to arrange buying an affordable one.
(Posted before you corrected the sex and step bits)

He’s at uni