I was under the impression that if I should continue growing the trunk out if I wanted which wouldn’t be a good idea to include bonsai soil.I would personally clean the juniper of any unwanted foliage, making sure you choose the branches you want to keep.
If they are not in Bonsai soil I would repot them into a 2 1/2 inch wood box maybe 5x5 or so.
Dawn redwood needs a bigger shallow box or pot, and a repot in bonsai soil.
Just my opinion.
Thanks