I agree 100% on the need to have an impartial executor, or push to have your friend be it, but that may cause hard feelings down the road. It will cost the estate about 3% of the value of the estate if your parents choose to have the solicitor be the Executor. That is what most solicitors charge. It will cost nothing if an impartial family member or friend is selected to do it. Either way, I think that it should be someone who does not have a vested financial interest in the case. My uncle chose not to go down this road when he wrote his will, and 10 years later it is still causing grief within the family.
When the parents die, and your friend forces the issue, and the house has to be sold to pay her her half share of what it is worth, that will probably cause hard feeling between her and her brother. But if he is (a) already exerting undue pressure on his parents to move out off THEIR HOME so that he can move in and (b) has already stated he does not intend to take care of them as they get older, even though they gave him THEIR HOME to live in, he is not someone I would be all that bothered about offending.