Seems a little early to bring in the pelargoniums. Mine are still on the patio in full bloom. I'll wait until the first really cold night. No need to cut them back once they are inside. Just hold back the water so they go dormant. Yes the new cuttings will be fine in the green house as well. Just treat them the same.

Hi, if your cold greenhouse isn't going to be kept frost free, there's not much chance of keeping them until next year, they need to be kept dry and frost free, then started into growth next year, if yo heat your greenhouse to somewhere between 45 and 50f they will carry on growing and continue to flower for you, Derek.

Bathgate is right . . . the main thing is to keep them fairly dry. The 'Regals' will make new roots through the winter, and should be fine in the greenhouse so long as it's not freezing in there.

they do need to be kept frost free and on the drier side if they are in a greenhouse. Mine doesn't stay frost free so they sit in the unheated conservatory over winter.
we have already had a ground frost and they were looking rather sorry for themselves.