AudioShare is pretty good for managing samples on iOS.
the most likely thing i can think would cause this is the filename or some folder's name in the filepath. certain characters and symbols aren't supported by max so make sure you don't use anything weird in your file/folder names. most importantly don't use any slashes '/' as it'll surely cause conflicts. easy way to test- If you place the audio files on your desktop, and drag them into re:mix from there, do all the sample names show up with waveforms?
to trigger multiple samples at once, they'll need to be assigned to different groups. (far right of the re:mix window there's a group setting for each row)