@wincarwoo
Somehow when you said "recently" I imagined a year or so.
Funeral not yet happened is very recent. The more I think about this the more concerning I find it.
Firstly the girls are newly bereaved of their father.
I suggest you enquire whether they have been offered any child bereavement services. There is Child Bereavement U.K. (which I think has Prince William as patron) that you could contact on their behalf in the first place.
I think they will need a lot of support - they will soon (if not already) be questioning the circumstances of their birth and it's possible they will feel resentful. Their "mother" is old enough to be their GREAT Grandmother! They cannot possibly be living a life comparable to other 12 year olds with younger parents who can take them swimming or play sports or other activities with them.
Secondly I wonder what the financial planning is?
For many 85 year olds there may be a discussion regarding power of attorney to protect their interests should they lose capacity. One occasionally reads of cases where children with POA abuse it and misuse their parent's funds, leaving them unable to fund care. I'm sure these cases are a minority, but normally I would expect the intention to be that the use of the funds has to prioritise the care and comfort of the older person, and if that means children get a smaller inheritance so be it.
But in this case there needs to be funds in place to secure the future of minor children. There's potentially a conflict of interest. There could be a situation of a person having POW for the 85 year old mother and the children's guardian seeking to establish their rights to funds for the future. It seems very complex to me.
I would make some tentative enquiries regarding plans for the care and protection of the girls with a low bar for contacting social services or even seeking legal advice on their behalf.
I know that some young children are carers but it seems very extreme in this case and entirely the result of ill considered future planning. Their rights need to be protected.