BDE.
There are many excellent sefarim. It’s interesting, I’ve seen this in a few families, that different siblings will get a different psak for questions (e.g. a relative who got married during sheloshim, one brother shaved, one didn’t, they had to come to a concensus about where to sit, etc.).
You need, and should have a rav. This is uncharted territory for everyone, and not just the first time they go through it, years can pass and people get rusty (not a bad thing; I hope you don’t go through this again for many years).