Hey Mittlillaego!
As far as i know you can give up to 6 accounts access to the Family premium but if u need any profesional assistance i can highly suggest that you head over and write to @Spotifycares on Twitter DMs they often reply within 2 days and provide great help 🙂
Hi, and welcome to the community!
No need to worry! With Spotify family, you keep all your accounts as they are and they are all upgraded to premium. You would share them the same way as if your accounts are entirely separate (ie, make them public and share the link). If you want to collaborate on them you can right click on them and click on make collaborative.
You can find more information on the FAQ.
Taylor