In need of advise please!!

I have two boys one is 7 and the other is 4. I can't seem to get them to stop wetting the bed at night, it's out of hand. I have tried making then clean there own stuff, limit fluids before bed, getting them up at night, taking away there things, pull ups make it worse. Been to doctors and no medical reason for it. Doctor claims it's pure laziness. I have talked with them, everything i can think of i have done. The boys have even thought it's funny that they pee and have said such things as "so what, it's my pee". And laugh about it. When we was doing pull ups they would laugh putting them on saying that they are babies and act like there a baby. And with pull ups they pee even more. So pull ups are out. I'm at my wits end with it. I don't know what to do anymore. There room smells there clothes smell even after there washed. I can't take it anymore. Please help with any advise. It has got to stop already. It's been an on going thing for the 7 yr old and I had the 4yr old potty trained and not wetting bed for a few months and dad didn't know he wasn't wearing pull ups anymore and stuck one on him back in Oct and he hasn't stopped peeing since. (These are my step kids, I have been in there life for 2 yrs now.)