My sister is a beneficiary on my late father’s will and is a vulnerable adult. What are my options?

I am the exector of the will. I have received all monies and had tried to pay my sister without success as not provided a bank account. She has schizophrenia and not taken medicine for a number of years. She will not answer the phone and is very difficult to communicate with. This has been going on since March. She has now gone to a solicitor and not only wanting to know what she is due from my late dad's will but also my late mum's from 2001. To be clear this was paid in 2001 but she claims not to have received. The will stated to put in a trust but at the time she and my dad agreed to having a lump sun of nearly 42k from memory. my issue is I destroyed nearly all docs a couple of years ago so cannot show paid and bank saying statements only go back to 2005. My sister is with a partner who I am sure is making all this happen so he can claim the money. she has said in past he abused her as well. What can I do to protect my sister? I would ideally like to put money in trust but will did not state this? My mums will was 18 years ago and due to mental state and husband she then had he spent all money when she was in hospital as had her PIN number.