By river cruise do you mean one of the multi night cruises up the Rhine? Or do you mean the one hour tours around the canals of Amsterdam?
If the former, they have real staterooms which can go someway towards protecting you against the bone chilling wet wind. If the latter, a lot of the fun is diminished when the sliding roof is closed and the windows steam up.
I've never done one in the depths of an Amsterdam winter, but I can tell you from a few trips there in March and April, if the sun isn't shining, and sometimes even if it is, it can get pretty nippy.
Amsterdam is the first stop for the winter winds off the North Sea.
At the ages of 15 and 17 it would be a good idea if you let the boys plan some or most of the days. It will give them great experience and take a load off you.
We have had two or three 16 and 17 year olds on here planning for themselves or a small group.