we just let things be - they come over when they want and when they don't i do the happy dance!!!!
my skids are 15 and 17 both boys. ss17 now has a job and a gf. they live 30 miles away. when they dont' come on the weekends for a while DH will contact them to at least do a meal together.
the way DH sees it - he knew as they got older they'd get a life of their own and quit coming over. he's not goign to force his kids to come visit if they've got stuff they'd rather do. kind of like teenagers still living in one house with parents, they get older and do their own thing.

I think the CO needs to be enforced. If their dad is paying BM hefty child support and wants to see them, he should be able to. They can invite their friends over to your house. That way, your DH gets to know what type of kids they are hanging out with. When these kids get out into the real world, they're going to see that it doesn't operate like BM does. Their dad should start preparing them for that experience right now, while he still can.

I have to say that I think most teenagers don't want to be around mom or dad - they just don't like adults - my SS lives with his BM full time - I had my share of that when we first got married - we are 700 miles apart - we always invite him for more than 2 weeks for the summer and he always refuses - he wants to be with his friends and not his parents - his mom is never home so of course her house is the best because there are no rules - he can come and go as he pleases she even got her rich boyfriend to buy him a car so she does not have to drive him around anymore - she actually told my DH that he needs to pay for half of a car because her life is too busy to be bothered with all of the SS's activities which is a joke because all he does is play basketball in a out of school league - so we said Hell no - you want him out of your hair pay for it.

My DH would like to see him more of course but we can't and he said he is waiting for him to be 18 and start to live for himself which I never see happening because if BM could wipe his ass she would. We have DD5 who misses her brother he comes to visit and then after about 2 days she is ready for him to go back in fact this time she did not even want to say good bye she just wanted him to leave - which confused her because she loves him so much but he was just horrible to her - he was playing with her and hurt her on purpose and I about killed him - so of course now that she has not seen him since August she can't wait to see him at Christmas - but I am sure 2 days into it they will be at each other's throats again. Now as far as your DS1 I am sure he loves his brothers around but being teenagers they will not like it so much - my sister had her third child when her two oldest boys were 13 and 15 and they adore their little brother but they would get sick of him as well and they are all from one family - I would tell the boys though that even if they don't want to come over for DH that they should come and visit DS because he is little and does not understand about the dynamics of teenagers so make a play that they need to see their brother every now and again - and your poor DH will just have to wait until they grow up and want to have a relationship with him. I think we all forget how we could not stand to be around our parents at that age just like they can't either. The only reason they like their mom is because there is no rules and it is probably easier there and no little kid running around - so it has nothing do to with DH just the whole being a teenager! Maybe you can talk to them about coming over for dinner during the week and at least a little of their weekends.

I just remembered when I was a junior and senior I was in so many activities that I did not even get home until after 9pm - so they may just be very busy.