Deleting a family member from sharing

If they have downloaded something then it will remain on their device. If they are using a subscription service for which the primary subscriber is a family member, they should make sure they have their own subscription. This is critical if it is an Apple Music subscription.

Read Leave Family Sharing - Apple Support

Go to the section --> What happens when you leave Family Sharing?

As log as it is on their phone and not in the other person's iCloud being shared. For example, if you download an app that somebody else purchased, the app will stay on your phone but you won't be able to redownload it or update it once you leave FS. If you listen to Apple Music as part of a family's subscription you won't be able to once you leave. If you downloaded a music track purchased by a family it will stay on your phone but you cannot transfer it to another device, nor can you redownload it. If it is something you generated such as a document then it will stay.

If you participate in a fmaily mamber's Apple Music plan, make sure you have a personal subscription before you leave-- that is unless you don't care about things associated with the subscription.

iCloud storage is a bit trickier. The best thing to do is make sure you have a personal subscription before you leave, otherwise you are essentially downgrading your plan. If you downgrade, make sure you read the section "What happens when you downgrade or cancel iCloud+" in this support article Downgrade or cancel your iCloud+ plan - Apple Support