Roles

First, Apple IDs are not meant to be shared. Everyone on a Family Sharing Plan should have their own Apple ID. Then the only information that is shared is information YOU choose to share (there are some restrictions on a child's account).

Family Sharing - Apple Support

Set up Family Sharing - Apple Support

Use your own Apple ID for Family Sharing - Apple Support

Family Sharing and Apple ID for your child - Apple Support

If you share an Apple ID with someone else, then that other person can indeed "mess with your stuff" (and there is no way to prevent that).

Dmt10101 wrote:

How does the role of adult work with the family share plan? We have an organizer and then I am on the same account as an adult. Can the organizer mess with my stuff without it alerting me or anything?

The Organizer cannot "mess" with anybody's stuff. Period. As an Adult, you are eligible to approve "Ask to Buy" purchases from minors. That's it.

Family Sharing simply allows you to share media, calendars, photos, iCloud Storage. The Organizer pays for everything unless you have an iTunes credit on your Apple ID.

The only other thing that an Organizer can do is to disban the Family group or "uninvite" Family Members.

Cheers,

GB