It's always seems hard to deal with people. Here are few thoughts that I'd like to share.
Blame does not fix bugs, the outcome is important, not the credit, the blame, or the ongoing intellectual superiority contest.
You want to focus on fixing the problem, instead of blaming others.
Criticize ideas, not people, keep it professional, not personal.
Ask questions that allows someone to figure out the problem for themselves.
and there is one more thing, negativity kills innovation so be constructive.