The bigger pouch comes with the BL-P1 Accessories Kit .. it includes all the diffuser and shades that go on to the light, so the pouch is to carry all these together..
should be fine, just leave the 35mm on the xt3 and the other 2 lenses will fit with the dividers.. here I did a 3d model to check if they will fit app.vectary.com/p/3yStRnchOkIniGdNpFjF2b