Some of the responses here have been good. But I don't agree with all of it. Yes, it's the age, but there is more to it than that.
I'm a stepmom of a 22-yr-old young man. DH & I have a 12-yr-old boy and 8-yr-old girl. So what I'm about to tell you is meant to be helpful. I'm not better than you.
Moving away was a huge mistake. (I'm saying this not to crucify you, what's done is done. But for anybody else reading to learn from this and see what results.) Even if it were to benefit one person (you and your daughter) it took a huge chunk from 2 other young people, who needed their father more.
If we got divorced and DH * had to * move away to another state or country for work, I would move also, so our children could have close, constant contact with their father. Trust me, I wouldn't be happy about leaving the place I love, but if it helps everyone, then I'd do it. (I know he wouldn't do it because his new wife wanted to, because the needs of other people are involved.) My dad died when I was 4. Having your loving, devoted father around is such a gift. I wouldn't want to deny anybody that.
So yes, the boys lost their father, to their new (lovely, sweet) wife and new baby. They were left. Put yourself in their shoes. Imagine your husband had no children, divorced you, remarried a sweet woman, has a new baby and moves away with his "new family." How would your daughter feel? Is that cool? No, it's not.
So there is that.
My husband's son moved in with us with he was 17 (long story). He lived in another country with his mom up to that point. My husband used to fly one weekend a month to see him, every month. Sometimes the ex-wife wouldn't let him see his son. That didn't deter my husband. You can't let that kind of stuff deter you when you are talking about flesh and blood. (And he flew his same age-cousins once a year for a vacation to help them bond and get to know one another. It worked. These things didn't just happen. DH cared enough to see it got done. And trust me, there were plenty of times DH could have sat in his own pity party. But the stakes were too high and he had to fight through a lot. His ex-wife's family was definitely trying to poison the relationship, prevent access and generally keep the boy from his father. DH made it plain to them he wasn't going to give up. SS saw living proof that dad did love and care for him.)
My husband spends every Saturday or Sunday hanging with his now-grown son. He has mentored him and guided him and this has been INVALUABLE to their relationship and SS's development. He's in college, has his own apartment, has a part time job. D is helping him, counseling him and not enabling him.
Right now, we could move out of state and DH could get a higher paying job. He wouldn't dream of it. Our lives are settled here, but primary reason is that he'd have to leave his son. SS is not ready for that. What's more important? More money? A bigger house? More stuff? Or the people you love? (Oh and BTW, SS was very envious of my son when he was a baby. Pretty normal and understandable. Over time that has changed. Both of my kids have a warm relationship to their big brother. And I'm so glad he is around. When I was sick a few months ago, and couldn't drive, and DH was away and I needed help, I asked SS for help and he was ready and willing to zip over (50 minutes away) to help me. Turns out I didn't need that, but that kind of devotion doesn't just happen.)
YOUR HUSBAND IS DISCOURAGED AND READY TO GIVE UP
Please God, no. What a huge mistake. A relationship is built over time. Your husband needs to PURSUE THEM (sorry, I don't have italics). Over time, it was communicated strongly to your stepsons that they came 2nd and 3rd and last. Now with other competing interests, they'd rather be doing other things. This has nothing to do with their mom. This has everything to do with the non-relationship they have with their dad.
Yes, they are teens, but it's your husbands job to maintain the cord of communication. And playing phone tag isn't working. They need face-to-face time and a lot of it. Once that's there, he'll get more respect and returned calls.
"We're not sure we can see you this Christmas." Means, "eh, we'd rather not. We'd rather spend it with other people."
Given that there is no relationship, that shouldn't be a surprise.
At this point, he should fly down for the weekend once a month or more. Ideally, alone, so he can focus on rebuilding the relationship without distraction. Once things are warmed up between them and his son's KNOW that dad cares as much about them as his new family, you and your daughter can start to visit. Then you can build that.
This is going to very hard for your DH because it hits all his buttons and he's telling himself lies (they are ungrateful bums).
He does need to sort through his issues as well.
So my advice to you is not to talk to the boy's yet. That's not going to go far. You need to work on building up your husband. Get him over there. Encourage him when he feels the door shut in his face. Or maybe just you two go, but let him be with the boys.
Your husband's main job is to rebuild the relationship. That is the primary thing here. Visiting for Christmas once a year is nothing. Thankfully, your head is on straight and you care about everyone involved. So you can do a lot behind the scenes to support them.
And don't talk to the mom. You're right that won't go off very well. That's not what's needed here. Over time, when they all see Dad's devotion and TIME, nobody will have to "talk" to anybody.