You can hatch these eggs fine. The immediate health of the babies is not the issue. The problem that many people have is that these poults would hatch smaller than their peers and then get off to a rough start. If all your poults are the same size, I don't know that you would have a problem. The second factor involved is that the parents are not proven and might be weak genetically. Therefore, hatching from young stock could cause you to perpetuate genes, etc that are not good.
If you have a rare variety, however, you should probably hatch whatever you can in case you lose a bird and then no longer have access to any more. First, build up your flock, then use time as one of your culling factors.