There Montipora eating nudibranchs ,in tank is very difficult .. Out of tank u can dip in TLF revive, but there eggs will survive so you'll have to do two Hail Marys and one our father..
Just montipora... digis are montipora. They won't bother other corals.
They are really hard to get rid of. If you have relatively cheap or small montis, just toss them and don't bother trying to dip and put back. Not worth the effort and they may come back. The dips won't get the eggs.
Tidal Gardens had a video on youtube all about reef pests, identifying and what to do. It's been a while since I saw it but it might be worth your time.