The Wildling obvious want to escape the white walkers and other dangers North of the wall. Why not do a trade off. The Night's Watch numbers are down big time. Mance is also a wise leader. Require Mance and 500 of the best Wildling fighters, including all the giants to join Castle Black and the Night's Watch.
Require the rest to join Stannis army to fight the Boltons. Then the women, children and sick can start the village and farms just South of the Wall.
That is a win for everyone. The Night's Watch gets much needed skilled reinforcement. Stannis gets more troops for his conquers of Westros and the Wildlings get to go South of the Wall!
Yeah, how did Stannis Army get NORTH of the Wall?
He sailed to Eastwatch-by-the-Sea (there are many unmanned or poorly manned Night's Watch castles along the wall besides Castle Black). Eastwatch is the easternmost castle along the wall, and Stannis and his army then traveled west along the northern side of the wall in order to take Mance and the wildlings by surprise.
Are you getting this from the books or from summaries of the show? Just curious if the show is still following the books.