What To Do In The Event Of Deceased's Next Of Kin Being... Skipped??

Briefly, my dad died (no surviving spouse) in a state where next of kin is surviving children. This happened a few months ago, but I just now have the strength to really address how I felt about it. Everything defaulted to his parents - decisions regarding his house/cars (sold or taken back due to payments), accounts, decisions regarding cremation (they cremated him without asking his children/asking if we'd like to be present OR have his ashes), personal items (I was allowed to get only a few of his things by asking their permission and still afraid to ASK for his other items they took out of his house bc I'm afraid they'll say no).

Legally, I know how this was handled wasn't the best - I'm a lawyer - but I'm unsure what I could do now. I know there's nothing I can do about him being cremated, as pissed as that makes me. But I would like his personal items, autopsy report, and more information regarding his remaining estate (just the current affairs, I'm sure the house and cars are gone now and I don't necessarily want them anyway). I did receive a life insurance payout (that I believe they probably received the other half of), but I believe the only reason why is bc it didn't go through the parents.