Regarding #2, this is simply what happens when you have to play Rielly against top competition. He can't handle it. It's definitely not a TJ Brodie problem, he's actually been fine. It appears teams target Rielly's side because of how bad he is on straight man-to-man defense.
Muzzin is the best defensive player on the team who also happened to be a physical beast. There is nobody on the organization who can replicate what he brings. The whole team is going to suffer with his absence just like it did last year.
Acquire a D who can comfortably play against top competition alongside Brodie, find another cheap Lyubushkin type to pair with Rielly and play them against lesser competition, and wait until Liljegren returns to reunite the Gio-Lilly pairing.
We have virtually no cap flexiblity and this is about the best thing we can do to improve the D.