Is this financial abuse of a vulnerable person(s)? Wales

I’ll try and keep this as short as I can!

My MIL’s sister has advanced dementia, and my MIL has deputyship over her estate (houses and items worth over £750k with no will). Her sister has 1 daughter who is has severe learning difficulties and is married to someone with similar issues.

The daughter and the husband aren’t very good with money and the MIL and husband have been helping them manage by sorting their finances and limiting the amount of money they have access to (the husband goes missing for hours, spends the housekeeping money says he has no idea where the money has gone).

As the in-laws are quite old fashioned, they have been taking the daughter down the bank and getting her to move money around to limit the amount they can spend, having the bank statements delivered to their house in the UK, threatening the husband that utilities will be cut off if they spend the housekeeping money etc.

We have spoken to them about it looking like/is financial abuse but as they aren’t stealing money off them they can’t see the situation they are in. They are waiting for social services to carry out a capacity assessment on the daughter I believe, as when the mother passes she stands to inherit the estate.

Can anyone give me a legal view on this so I can try and talk some sense into them!!

Thanks