You can pot up in mid to late fall if you like, as the leaves drop. I am not familiar with the soil mix you refer to but as long as it is very barky and textural, it should be OK. The trees are a little young to go untended outdoors all winter unless in a very mild winter climate. You don't want to keep them indoors but they should be kept somewhere that stays just above freezing.

As to 'maintaining their shape", the Red Filigree will naturally attain an umbrella shape but unless you want that umbrella to form very low to the ground, I'd consider staking the tree upright for a season or so. Just until the main stem (future trunk) attains a more upright habit and a somewhat taller stature.

The MY has its own unique form and I wouldn't do anything to it. It will slowly elongate and develop additional stems/short branches with those dense clusters of leaves. The mature form of that cultivar is rather stubby and asymmetrical and your baby is clearly showing those characteristics.

IMO, both trees are too young to be planted outdoors any time soon. Those look only like 1 year grafts and I'd prefer to have them grow on in containers where I could monitor them closely for at last a couple more growing seasons before planting inground.

GG48 thanks for the reply, I live in South East England (Kent) and normally the winters are wet and mild and the temperature will only maybe drop below freezing for a couple of weeks during the winter.

I will take your advice and will probably overwinter them in the greenhouse or a cold frame, they can stay in pots for now as we plan on moving home soon.....looking forward to seeing the MY grow, and wondered if these are a very slow growing variety?

Mine is growing faster than I expected but it is considered a dwarf form so growth is slow, relatively speaking :-) And new growth is short, with not much space between nodes and with leaves clustered/layered at those nodes. So new growth does not look significant compared to most other cultivars of JM's.