It seems as if he's waiting for you to bring it up. He already knows you're upset (concerned) but he's acting as if, no news means he's won. If you bring it up, I promise he will be just as defensive and will say everything and more, about how HE feels, totally negating your feelings or those of his sons and your son, not to mention accusing you of not caring about his feelings at all.
I'm not a mind reader (and rose is right...you really only get to know a man -or woman- when you spend time with them. Texting/email/messaging is a nice start but that's all it is, a start). The reason I feel I know his next move is based on your comments just now regarding the call. And from my own experience.
He obviously knows your hurt by his neglecting a subject that is very important to you...and that is necessary for him. So he'll wait you out, and will act completely surprised when YOU bring it up, because I honestly don't think he will. He's challenging you.
He's happy because in his mind, he's won, because he got quiet and ended the conversation........annnnd you didn't bring it up later.
Bring it up before the trip. Waiting until you get there will be....WILL BE .... a horrible mistake. Be as non-threatening as you can...almost offhand i.e. "have you given anymore thought to what we were discussing about the kids?" Sound cheerful.....sound like you believe he's relented because your thoughts are the wiser ones. If YOU believe it, it won't be that difficult to pull off. It offers him a chance to 'man up' as it were. I don't think he will, but we'll give him the benefit of the doubt.
Honestly, I think he'll be pissed you brought it up and then probably angry when you stand your ground. But it's better to know now. Just make sure you have a 'holiday back up plan'....cause this one may fall thru.
I feel so bad for you.....I can see the road you're on because not that long ago, I traveled along it. It was awful. And I knew my bf for years. I'd spare you that.
Take care.