Complex inheritance problem, advice needed

[honey59]

My mother-in-law passed away in November 2018, some six months after her cousin died. The cousin left £10,000 to my mother-in-law in her will. Since my mother-in-law died without a will, intestate rules come into play, but this is where it gets complicated. She had three children, the eldest of which closed her bank account without telling the other two (my husband and his sister) and withdrew all funds. The distribution of my mother-in-law's cousin's will is still ongoing. My father-in-law received a smaller sum. He insists they divorced years ago, but does not have any divorce papers or dates. I have tried to trace records online, but have found nothing so far. The solicitors handling the will are withholding my mother-in-law's inheritance, as without proof of the divorce, they can't decide whether the children or 'husband' inherit. I strongly suspect that the divorce may not have been finalised, which would mean my father-in-law would inherit. The solicitors, who have dragged their feet for some time now, sent him a letter along with his cheque asking him to sign a declaration to say that he would not make any further claims on the estate, despite also implying that he may stand to inherit his late wife's share. He is nearly 86 and is very confused and upset by this and I am at a loss as to what we can do next. If anyone could offer any advice I would be extremely grateful, thanks.