Hang in there with them, don't get discouraged yet, they are only 8 months old, still babies. Like the first reply said sometimes the ones late starting turn out to be the best. Hunt the ones that aren't going by themselves with some older running dogs, don't hunt them together for now because one is probably messing up the other and vice-versa. As long as they have a tag-a-long buddy to run around with they probably will be less likely to get in the hunt.
Hope this helps and hope they turn out well for you.