Underboss,
The screenplay did not take us in the direction of your theories. No one knows if Fredo gave them info about the estate. I believe him when we told Michael he had no idea there will be a hit. The only thing I can see they used Fredo for in getting an insider track on Michael's next move (i.e, Is Michael going to make the deal with Frankie or bring his boys?).
All Fredo wanted to do is carve an income outside of the Corleones. But that does not negate the fact that Fredo went outside of the family.