Mum keeping whole of grandmother’s inheritance

If there's no will, the estate (which means the value of their house, savings and possessions) are divided according to intestacy laws in the UK, and if there us no spouse, the value is divided between any surviving children.
So it seems the mother of OP and her aunt have received the value in accordance to the law.
It would have been nice if your DM had offered you some kind of moments from the belongings, but she is not obliged to.
You can check if there was a will (or admin) on the Gov website regarding probate.

You are absolutely unreasonable. Get over yourself. And the money. If she wanted you to have it there would have been a will to say so.

Yep, hopefully it will pay the IHT due when the mum and aunt pass after they broke their promise.

Hopefully your mum and aunt will have invested the £100k wisely and when your mum passes she will leave you a nice amount. If your grandmother left no will then, word of mouth means nothing.

I see where you’re coming from especially when they both said you’d get the share and then none of you got it.
even had they given you the amount they first expected.
id sit down with her and just say something like “you know when you said that we’d get the share of grans assets, well I know it was worth a lot more, but are you not going to stand by the original offer of what you thought it was worth? Only if I’d known you would back down, I’d have kept something from grans items, but as you said we were getting the money, I would have liked to have purchased something in her memory”

All your points, plus it gives the estate a decent tax break

When my DM was sorting through GM’s estate she found out a non bio grandchild had taken her to a solicitor and had the will slightly altered. As DM was the main care giver, she was aggrieved that this occurred when the GC had little to do with GM on a weekly or monthly basis anyhow.

You mentioned your mum is still very raw about dealing with the estate.

im wondering if debt appeared that was unexpected or that your mum felt was unjust and she was left to sort the mess out by herself.

it might explain her position somewhat…

Exactly.
I get it, @Virgoschild . My wealthy childless uncle promised my dad he'd "look after" me and sibling in his will. He didn't. Sibling and I both went through very tough times financially and any windfall would have made a huge difference. We didn't feel entitled, it just would have been better not to have been given that false promise.
A close relative promised to leave my kids a decent amount of money in their will. They left them (and me) nothing.

What hurts is the broken promise - you have the feeling of gratitude that they would give you that gift, and the hope that you can use the gift to make things better, only to find that it wasn't real.

If you are left money, or it comes to you through inheritance, you aren't 'grabbing' it. It's yours. If others say, well you don't need it, and actually it would be great if I had it instead, that's 'grabbing'.

Not everyone has the sort of relationship with parents which allows them to talk about money. My DM was always secretive about money.

As a reaction I am open with my adult DCs. If I promise to give them money then I give it to them when I promised to give it. No game playing.

Your mother shouldn't have told you she was going to gift you £4k and then not do so, presuming it was still within her means. I wouldn't risk an estrangement over £4k though, most likely money will come to you eventually when your mother dies (if not swallowed up by care home fees before that).

However, you went from talking about £4k to a large lump sum for a house deposit. That was NEVER what was offered, so I think you need to get saving yourself on that front.

Actually I think the aunt and the mum are being grabby. When you are being given the original amount plus £50k when you are already set up financially then the extra few thousand out of that £50k is a very small percentage.

It’s all very well saying your time will come but the situation these days is very different to previous generations. It used to be possible to save a deposit within a couple of years if you were careful with spending. The mum and aunt are already sorted so that money isn’t that important to them. For the OP it would be life-changing to enable her to get her own place. Not much help waiting until your 50s or 60s to get that money - you need it when you’re younger.

Being able to give out treats is an ego boost for the aunt and mum but isn’t really beneficial to the OP’s financial situation.

I agree xx

My Dad once promised me the family land as I was the only one that worked it for years - he left it to my brothers who had no interest in it. Talk is cheap. I never held my Dad to it - he did what he wanted to do.
Still baffled how much has changed with adult children feeling entitled to a house deposit. The cousins have taken out a mortgage and do they think their entitled to someone else should paying it off for them?

Finally I wonder how well off your mum actually is - how good is her pension? Maybe she has realised she’s not as financially invincible as she initially thought when she offered to share the inheritance. Your mums earning power is more limited due to her age.
inheritance really does bring out the ugly side in people.

Has she reneged on it though, OP says she is treating her. Unless OP is able to set out the conversation and other conversations my bet is that she misunderstood what was said.

It's her money. She shouldn't have said her plan was to treat you and then renege on it; that was unkind and unfair. I wouldn't say anything though. Just wait. You'll get it all eventually.

Has OP been back to explain exactly how the conversation went and who was involved?

How come the cousins and her brother havent also raised this, is this because it wasnt actually a promise as such, so they have different expectations to OP

Did OP mis understand something said?

I said "similar" - not "exactly the same"
*Sigh.

unless there was a will which stated the grandchildren should each receive x amount then the money goes to your mum and aunty. if they promised you an amount then backtracked thats bad but not illegal. Sorry but you are coming across as extremely entitled. No-one should expect an inheritance

She might be getting her ducks in a row to leave your dad. It's surprising how a lump sum of cash, that removes a woman's financial dependency on a man, can make you suddenly intolerant of the things you've been tolerating for years in a marriage. Happened to me. It was like a spotlight was suddenly switched on & shone on everything I'd been putting up with for years.

As others have said, it’s legally your Mum and Aunties money, but if she had specifically said 4 grandchildren would be gifted a share of £16k, which then transpired was worth £100k - why not gift the original amount?

Grandchildren would have the £4k they expected and Mum / Auntie would still have £84k more between them then they were expecting - seems a win -win ?!

These situations are delicate, by law your Mum and an auntie are the correct descendants without a will.

£15k to £100k is vastly different, I think if misc around £15k was assumed this would be the more likely amount to be split, £100k I would think too much. Leave it a little time, try amd bring the delicate subject up, but £4K is not worth ruining a relationship over. That or you could ask if you could have a loan, you’d assumed something and need it for something, it may prompt a memory, however very likely please remember she’s lost her Mum and is likely devastated and any mention of money will seem crass and she could be appalled. Normal relationships I imagine you will also inherit one day.

The inheritance was left to your mum and your aunty not you , if they promised you some money no doubt you will get it in time .
When my mum passed away we did get some money but the last thing on my mind was money! I was devastated with having to deal with funeral and probate and grieving for my mum . I didn’t want to spend any money initially as I and my sibling felt uncomfortable about it , it took almost a year at least that we started using it as mum had wanted . Maybe you should be giving your mum some emotional support instead of spending her cash!!!

That's a really shitty thing for your mum and aunt to do. I don't think I could look at my mum the same way ever again if she did that. Some people's true colours are shown when money is involved. A decent parent would stick to their word and would also not want to see their DC struggle whilst they sit on a sum of money they don't need.