Glad to hear they're happier with the extra space. Degus are excellent grudge bearers as you're finding out. With the extra space it could just be dominance fighting now and they may need to sort it out between themselves, but if they are drawing blood, they need to cool those tempers before being reintroduced.
Have you been swapping the sandbaths over? Remember the grottier the better to mix those scents.
He should be fine without the wheel if he's getting enough exercise outside the cage - its only temporary.