How do I talk to him?

My younger cousin, who is fifteen, was in an accident in the past year and injured his spine, losing use of his legs. He’s adapted quite well to a wheelchair and his cheerful spirit hasn’t wavered much, though I imagine sometimes he has to fake being happy for the rest of our sakes. I know that sometimes, he gets very depressed.
He’s been visiting our family lately, as we’re closer to him in distance than any of our other relatives and my siblings and I are in his general age range. But lately, the situation between he and my family has become awkward. We try to act like he doesn’t have a disability and treat him like any other normal family, but sometimes a circumstance arises where his situation is impossible to ignore. The conversation thus becomes rather awkward for the rest of the day.
I was wondering if there was any way to make him feel more comfortable around my house and become less sad and embarrassed about himself when he can’t do the things he used to.