Also what is the appropriate fertalizer for these mango trees?

Congrats on your new Mango trees...make sure what ever potting mix you use that it drains well, you can add some of these ingredients to help make the mix porous and drain freely... perlite, small pieces of fir or pine bark, crushed granite. If you do a search you will find many different mix that people use. Don't use a mix that stay wet and takes a long time to dry especially since your mango tree will be living indoors for several months in the winter... mango roots don't do well in soggy soils...it could cause root rot.

As far as fertilizer goes, you can use slow release like Osmocote or something similar or use 1/2 strength balanced liquid fertilizer or Dyna Gro Foliage Pro, many other great ones out there as well. Just use it at a "weak" solution so you don't over fertilize...young mango trees don't like to be over fertilized. Fish emulsion is another good one to use...again at about half of the recommended dosage. Once the weather warms up and you can bring them outdoors and the tree is growing you can fertilize them a little more often...usually in the winter I would not fertilize them often and only lightly...

Good luck!!