You don't mention a tup. Are the ewes already tupped? If they are, then it shouldn't hurt to put the ram lambs in with them.
However, if they are not tupped, then it could / would cause a fight when one of the ewes comes a-tupping, so in that case, I'd put the ewes and ewe lambs together in one paddock, the ram lambs in the other, until the ram lambs go.
Otherwise do you have a stable or something where either the ram lambs or the ewe lambs could go?