Its not that awkward, it's easy to see some of the things you can abuse. If your cousin gets in front by a stock, try having him grab one of the opponents so you can both Fsmash them. Also, try to get him in a high controller port, best would be port 4. If he grabs then, you will smash only your opponent away. Otherwise, if he's on a high port, you'll smash him away, but it might be worth sacrificing, you could get a kill in at about 60-70%.
The bananas are easy to abuse with Ike as well. Just use his Usmash not his Fsmash. If the Diddy hits opponents towards you, abuse your ftilt and bair. The lag on the ftilt should matter just a bit less in doubles and the bair is always a good follow-up.
As long as you're used to each other and know what the other player will do, you should be fine.