My dogs stayed with my friend in a 3rd floor flat in Berlin for 8 months (waiting for pet passports) on their way from south africa to the uk. They adapted very well - no problems. So long as they have enough stimulation and exercise, the garden size shouldn't bother them. As it is, I don't leave my dogs outside on their own - besides, they follow me everywhere. So during winter they mostly go out in garden for wees, otherwise it's walks in the fields. They have loads of opportunity for free running and playing then. As already mentioned - they're really adaptable little dogs who just want to be with their people. All the best with your move.