Roh594
I think it's best to keep them in vampire form anyway, at least give everyone a half vampire and half human form so they can enjoy the good things of a human (sleep, eat normal food, have kids, etc) but keep the good things from vampire (strength, speed, etc). As for the world of Pandora and the Navi, it would be nice for him to have grown a Navi body for each of them so they can enjoy the wonders that the world of Pandora has to offer. But let it be them using a body through the neurotic link and not turning them into a Navii. You can even use this as a way to make them experience what it's like to be weak again (physically), like a stat reset, because if they're too strong in this world I think it would take the fun out of all the adventure and dangers. of pandora. As for your gifts, it's up to you whether they keep them in Navii form or not.
it depends on if you want to use it as a plot point, do they still need to shift into navi bodies, if so do you make it permanent and do they lose their abilities doing so or do they become even more enhanced due to becoming a being of nature so it depends on how far you want to take it within the plot