For starters, the fact that he cries is very very healthy. If he's started listening to Xmas music already (in October?) means he's getting mentally ready for the holidays without his dad . . . And if he cries now, it'll probably be easier than you expect when the holidays finally do hit. I remember a friend whose husband died of cancer -- and she said that she expected T-giving and Xmas to be very difficult with her and the kids, so she had steeled herself to get through it. . . .which she did, better than expected. It was after that, when some little incident would trigger a memory that she'd break down and lose it. These kinds of things happen, though. It is a part of losing the company of someone we love, and it is normal, and healthy. The "unhealthy" grief pattern would be to remain stoic and not express your emotion, or tamp it back to the furthest recesses of your mind so you don't have to face it . . . to walk stalwartly toward the holidays, thinking how much fun they will be, etc. . . when reality is very very different from that.
Perhaps if you spend Thanksgiving with some new and different people this year ? And talk about Christmas when you get closer to it. Ask him what he thinks would make it easier on the kids to be without Grandpa. . . Do you want to do it the same old, same old, or jumble things up with a "new" tradition added into the celebrations -- with something new going on, that Grandpa wasn't a part of, it might take some of the sting away.
It is hard to sit back and watch men cry. We don't expect them to in our culture, so we don't know what to do when they do. But crying is okay. Give him space, knowing that each of those tears brings him closer to the time when he can square his shoulders and walk through life a little taller than he did before. Know that the fact that he can cry in front of you shows a huge amount of trust in your relationship, and honor that trust. He's lost his best friend and his mentor in life, so he probably feels as if he's lost in the woods somewhere -- but he'll come through. Allow him these sorrowful times, and continue to welcome him with open arms back to the living -- share your lives with him, the joys and funny things that happen with the kids during the day, ask about his life at work, etc.
Most counselors say it takes a full calendar year to process the grief and another year after that to really more on. . . so do what you can; be encouraging and supportive, and keep the family on an even keel while your husband takes a little time out from time to time to grieve his dad. You'll get through this, and so will he. But there is no instand fix -- it takes time. Lots of time.