Seedling care - should I repot?

[avisignis36@gmail.com]

Good evening everyone!

I have several seedling orchids of various genera (cattleya hybrids, dendrobiums, oncidium intergenerics) that arrived potted in sphagnum moss. Two of them (Howeara lava burst 'Pacific Sunrise' and Ondonticidium Rex's Luck 'Firefly') arrived with wrinkled pseudobulbs, were unsteady in the pot and had some visibly dead roots, so I went ahead and repotted those and both of the root systems were 90% dead. Both also had plenty of new growth and seem to be doing alright now. All of the other ones look pretty healthy, though I do see a couple dead roots on one of the catts and a dendrobium. Should I just go ahead and repot all of the seedlings from this batch, and if so, into what? The two I already potted I used a mix of sphagnum moss and XS orchiata. Any other care suggestion are welcome, I'm a newbie! The sphagnum moss seems really densely packed, and it makes me nervous of overwatering...