Lin, whew it does sound like a sad situation.. what ages are the boys? it makes a difference from 13-19

It's real hard to give advice not knowing the parties involved and hearing you say that dad isn't much help, assuming he's trying to make this marriage work and partly because as you say he isn't home a lot.. but I'll leave you with just a thought.
It seems you have taken the boys into your heart and that they (one or both) have confided in you? If that is the case maybe you can help more than you realize just by supplying them with an adult they feel that they can go to talk to, just knowing that there is someone that will listen and care for them to vent to. And you being so compassionate for them will be able to give them that and possibly keep them in the right track as older teens can give up and become rebellious and lost so it's an important time in their lives and I'm glad they have you at least to give them a little guidance where the parents aren't. Also, you may try to get them to sit down and have a heart to heart with their parents.. sometimes things are unsaid that needs to be.. sometimes in the turmoil they don't feel they can.. but if they approach them in the right way and let them know they really would like to work things out so that they can all get along.. a good heart to heart can't hurt. All good parents want to know they sometimes just don't take the time to ask in their busy day and maybe if they sit down and talk without accusations just expressing feelings with an open mind to try to accept the new mom and make the new family work it just might open the parents eyes a little. Hope that helps sweetie, but glad you are there for them and since they know that at least they have one person they can turn to.
Good Luck Lin <3