On the android front you can cheat the downloads by making each chapter its own archive (rpa). I don't know explicitly how it works since i haven't made a ren'py game, but i know it can be done. Then they just have to download the core android launcher, and the RPA file for each section you do. If it's going to be around ⁷ gb total without compression that would be up to 3 rpa and a one gig core file. Or since there's no reason to limit the rpa to 2gb (as it's not an apk) then a 6 gig rpa for the full game and a 1 gig "demo" launcher/core.
Most of the Android porters on f95 use RPA for really big games now, so it should be easier to find out how than before.
But for consistent update purposes I would suggest keeping the currently coded content as the core apk file and finished chapters as rpa. Makes it simple (and small) to update on android still, and both you and us would only have to deal with a RPA after each chapter so should be simpler too.