The 16wk bucks would be ok to par up if they havent started mounting eachother, you would have to keep a check on them cos at three mths roughly they will neen the snip.The 8 mth buck is to big as you say and it would be better to wait until the does were about 3mths.it would help to know how long the buck has been done and how old he was when he was done, because if bucks are done young they loose the urge for mounting a doe and could be paired up sooner. A buck that knew he was a male will probebely carry on trying to mount a female for a long time, so could not be trusted with a very young doe. val