If you wait until the leaves drop to bring them in, I would think you could prune as much as you need to.
I sure wouldn't prune any more than you absolutely need to, though! You'll set them back for next year if you prune too much.
What are you going to do next year when they're twice as big?
Eventually you want a small tree, right?
Ask for a greenhouse for your next birthday, maybe?? There are inexpensive ones available.
