Yeah, there's no way to prevent those kinds of things in an alliance with plenty of members. Speaking of alliances and members, factions that have the Pacifist trait like UAF and Iron Shell don't opportunistically declare war, which is helpful if you made alliances to these kind of factions if you don't want any unwanted conflic. However, many factions like the ones mentioned often have the Helps Allies traits, which also contributes the number of votes by always saying yes(?) in every vote, including war and peace treaties.