It really depends on what the solicitor says and how the sisters react. My personal view is that you need a good solicitor on board who will take control of the situation and start to move it in the right direction. I would hope that you won't have to take legal action, but it sounds quite likely.
You definitely need a witness statement from the solicitor - however, he is going to be quite circumspect in the way he words it as he has not acted particularly well.
You really do need professional advice - there is a limit to what can be done over the internet without seeing the papers and being in full possession of all the facts.