The whole "co-founder" is more of an egocentric term in this case. In the end, does it make your product better or worse if they are founders? It seems like a

The whole "co-founder" is more of an egocentric term in this case. In the end, does it make your product better or worse if they are founders? It seems like a waste of focus to even worry about it. But if you must, I would consider the fact that being considered a co-founder might give them a lot more mental ownership and extra motivation when the times are tough.