All have iPhones at moment. Thinking of joining Apple Music family plan, which allows 6 people in same family. But will this still allow someone in the family plan who has an android to still be part of the same family plan?
Yes. You need to use Family Sharing to get a Family Apple Music subscription. Each family member has their own Apple ID. Once you join a Family Group that has an active Family Apple Music subscription, each Apple ID has Apple Music access, and they operate as individual accounts with a single $14.99 payment billed to the Family Organiser (in this case, you).
The Android user then simply logs in to the Apple Music app using their Apple ID.