"I haven't been backpacking in 20 years, I'm taking my two sons (20 and 14) for their first time. Is this a good idea? What's the chance of losing the trail in the snow?"
Andrew, how many of your sons are you prepared to sacrifice? (joking)
In a couple of weeks, the streams will be different, probably a little lower. What you and your sons might do now, for preparation, is practice stream crossings in shallow water near home. Use 50-100 feet of light rope. With two people anchoring and one person supported, it can be done. At a minimum, you will learn your limits.
Then, when you get to the real streams, you are prepared to go for it. The real stream may be much faster and much colder.