Most folks i know use a laptop for this sort of thing .... it used to be
that assigning hardware faders to ipad apps was not the easiest or most
reliable thing to do .... although there are some excellent ipad apps
for sound generation ( synths , sequencers , virtual pianos etc ) but
you have the forte 7 so .... ALSO .. Apparently forte 7 has an internal
input that you can mix with your realtime performance ... you might want
to check that out ...http://kurzweil.com/product/forte7/
anyway,
There are all sorts of Ipad to usb midi cables available for the ipad.
https://snapguide.com/guides/connect-a-midi-usb-keyboard-to-an-ipad/
From there it's a question of finding the best ios app ... in your case
( if I'm reading this right ) to host your mp3's or audio files
Probably some sort of workstation on the ipad .... and from there MAKING
SURE YOU CAN assign one of you faders to control volume on the channel
that hosts the audio file.
here is a list of daws for ipad
https://www.musicradar.com/news/tech/14-of-the-best-ipad-iphone-ios-daws-and-workspaces-574065
.... as I said, MAKE SURE YOU CAN ASSIGN A FADER to control volume
If you Keyboard is already hooked to something like a laptop ( to run
sequences etc ) you should be able to use any DAW to control your MP3's
or to properly mix your keyboard with the mp3's.
IF you do get all this sorted ... please take the time to tell the group
how you ended up doing it.
jjk
PS ) (IF it were me ... i would just set up the ipad on a stand and
control the volume from whatever you're using to host your mp3) or mix
via audio input mentioned above