You are effectively growing them like a bonsai tree so they really need a root prune and maybe a larger tub as well.
I would leave it until after Christmas assuming you are using them for display. Once out of the tub, you need to carefully untangle the roots and prune out some of the very thick ones or ones that are circling the pot. Make sure you leave plenty of fine feeding roots in place. Repot in fresh compost - for a tree like that I would recommend a John Innes soil based one, then make sure you keep them well cared for while they recover.
With fresh compost there is no need to feed straight away, but you could mix some slow release granules into the potting mix. If you don’t have them, just a basic balanced feed applied a few times next growing season would be fine.
