I have never heard of Brazilian redwood, maybe it's the same as a raintree. But my first advice would be to let those trees grow for about an year, and then repot them into a well draining soil (pumice, lava rock, perlite, vermiculite, zeolite, bark), really anything that doesn't break down (fast) and that also retains some water, some soils retain more water than others so do your research about the species of trees you have and their needs. Also please don't repot it into a small bonsai pot, it will stunt it's growth and it will take a looooooong time to finally see the tree you invision.
Seeing "Brazilian" in the name kinda tells you what it likes, water, sun, warmth and humidity, I'm not really big into tropical tress, but it may also really need fertilizer. After you repot it (also try not to take too many roots of a young plant), just let that baby grow for a few years.
While it's young you can maybe wire it's trunk to give it some nice movement if you want to, or you can just grow it as a straight tree. Also from what I've noticed from personal experience, when I wire seedlings they tend to grow thicker than a seedling which I dont wire ( I've only notice this on a few sweet chestnuts and on bald cypress).
If you don't have enough time to water these guys or someone to water them for you, I would either combine the well draining substrate with either some peat moss or sphagnum moss. Also, giving your trees a top dressing also helps, I have used fine sand and coco coir and they both do their job, they don't impede my watering (and also the coco coir just looks very nice).
