This has been a constant topic on Mamasource--do a search and check out past postings to other moms' questions about older kids and bedwetting.
One solution that comes up a lot, and sounds like it might be the answer for your older son, is a bedwetting alarm that senses the first hint of moisture in a child's underwear and gently wakes the child immediately, so he has time to get to the toilet. Other postings have mentioned brand names of these. I'm a little surprised that since your son is as old as eight, your doctor hasn't at least mentioned trying an alarm.
Of course, it isn't unusual for older kids to still wet the bed, of course, and it's a physical issue, not a behavior issue(as in "I'm going to be naughty and wet the bed" thing). Their bodies are still developing for a long time to come. I know other moms will come up with good suggestions about curbing the wetting or living through it. One thought that occurred to me, though: At their ages, your sons are old enough to strip their own beds and get their sheets etc. all the way into the washer each time the beds are wet. I would have them do this NOT as a punishment--don't make them feel guilty or like they're being punished for wetting--but clearly as a way just to ensure they know this is a responsibility of theirs. It might help with the "they just don't care that they're wetting" issue. Just be matter-of-fact about it when you tell them you have a new routine for the whole family. If it's middle-of-the-night wetting of course you don't expect them to haul stuff to the washer then, but the next a.m. they should as a matter of routine get everything out and into the washer. This might give them a sense of wanting more to work with you on bed-wetting, especially the older child.