I've known people who have decided to not be a third co-founder because of situations like the other two being brothers. The simple reality is that that no matt

I've known people who have decided to not be a third co-founder because of situations like the other two being brothers. The simple reality is that that no matter how professional people try to be, and how high the bar is, that someone is always going to be the third wheel in a situation like that. Also, in this case the OP mentions that they are already making decisions without him. If you've had a co-founder for years, there is no world in which it's OK to make decisions without them with someone you met 1 month ago. You don't even need to factor in the personal relationship for this to be sketchy.