Nope. You should not use that many Pokémon weak to fighting. 3 Weaknesses means Conkeldurr will enjoy the mass Mach-Punching on this team.
First of all, use Chansey > Blissey for the extra defense in Eviolite. You are really not missing a lot in 5 HP lost, for the better defense Chansey offers. Chansey will take Special Hits like nobody can, but will have a hard time fighting Physical Pokémons. You are right, this this is stupid because both Pokemon are weak to fighting Pokemon.
As for Snorlax, do not use it at all. His glory time has gone. Sure, with Thick Fat, it gets good resistance, but its defense stat is a disadvantage if your goal is to wall. Snorlax lacks a recovery move bar Rest, which will either cost you Sleep Talk, Chesto Berry or 2 turns. If you want a physical wall, then Skarmory is your buddy, resisting Fighting and sporting a nice 140 base defense.
As for Hydreigon, it is a good choice, because it can defend Chansey from Psyshock and strike back very easily.
Yes. Ignore both Blissey and Snorlax, prefer Chansey and Skarmory if you really want walls.
Hope this helps.