Yes they are adults making these allegations, but if the allegations are based on "recovered memories" then even most experts agree those kind of memories aren't reliable. There have been a number of lawsuits successfully won in the "recovered memory" cases.
So the police better have some actual evidence rather than just "recovered memories." If they found broken glass jar with no notes, and glasses during their digging, then I am sorry, that's not evidence. In a case where a murder is alleged, I think they need to find a body. Police have multiple people arrested, and I think it's only fair to ask what evidence they actually have.