Hi C.,
as you have heard from a lot of moms already, this is not an uncommon issue. My son is 8 and is now just starting to stay dry at night. He is now dry most nights.
We made the mistake of trying the alarm when he was 6, we read that most 6 year olds are not ready but he really wanted to try so we let him. Big mistake for us. He hated it and then did not want to try it again later when he first turned 8 (the age that was suggested as appropriate). Eventually he did try it, we had seen signs of less heavy pull ups for a while and he was motivated by a school camp approaching, and he wore it only a few times before we saw remarkable improvement, then it broke but he kept improving on his own. It was like he finally ready and just needed some assistance to learn the cues when sleeping.
Heavy sleepers are often the ones who take the longest to stay dry at night. As you have also read, there is often (though not always) a familial component. My mother, I discovered, was not dry at night until 10.
We spent several months washing sheets, blankets, and waterproofs when a counselor advised us that he would be better off without pullups. Eventually we had all had enough and he happily went back into pullups until ready to try the alarm again. Even then we used the trick of pullups over the underpants (you need to clip the alarm to underpants so it will detect the moisture) so that there was not much to do when he did wet. Now he is sleeping just fine without any of it. We still have a waterproof on the mattress below the sheets and probably will for some time yet just to protect the mattress against accidents or spills of any kind.
Please realise that very few, if any, children have control of this issue. Punishment and even reward programs rarely work. Do not be surprised if he stays dry when he sleeps away from home, he probably just doesn't sleep as deeply.
We found a book called "Waking Up Dry" by Dr Howard Bennett to be useful. It has sections for parents and sections for kids. www.bedwettingstore.com has some great resources and tools and a variety of books available.
Hang in there. We all make it through this though it takes longer for some.
K.