normally my kda isn't to bad.. usually early game my kda is pretty awesome the issue I have is late game where teams fall apart.. don't get me wrong i'm at fault for my KDA.
Your KDA doesn't really matter, you could be 0/0 and still be insanely fed if you farm well. Don't worry about your KD it's gonna get better with time. Focus on having at least 70CS @ 10 min and 160 @ 20min if you can manage to do that I guarantee you'll be bigger than everybody else in the room.
my issue is when my team is dominating then its like suddenly people get really big heads and start 1v3-1v5ing and suddenly the enemy team is fed.
Same as above, don't worry about kills. Only take kills if they are super easy and obvious otherwise don't bother, take towers, farm well and you'll be out of bronze in no time I guarantee you. In bronze people will fight 24/7 you don't want to be part of that. Your only goal is to get big, so don't fight unless you are super ahead. In bronze you can win solely off macro and pushing for objectives.
but I can't improve the mentality and team work of my team.
In bronze ignore your team, they have no idea what they are doing. Only follow on super obvious kills and never go for high variance plays, because they are coinflip. FARM FARM FARM get big , get levels get item push your lane win the game. Also play easy champions and play fewer champions ;)