The point here is to disable the Just long enough to get him without quarrel or less quarrel into his quarters and lock him there. Peter doesn't go long on care here; a few bruises, some discomfort are inevitable when bringing someone else to the ground, especially when anticipating that other person fighting back, which he does.

Edmund isn't in his right mind, but there's nothing they can do to change that. All they can to is attempt to control the consequences of it, and confining his brother is the only thing that occurs to him, even as he tries now to think of anything else they could do.