If i am sharing my location with someone else, how can they see both my apple watch location and iphone location?

Fairly new to this, please explain Family Sharing

Read Apple's support document What is Family Sharing?

With Family Sharing, you and up to five other family members can share access to amazing Apple services such as iCloud+, Apple Music, Apple TV+, Apple Fitness+, Apple News+ and Apple Arcade. Your group can also share iTunes, Apple Books and App Store purchases, and a family photo album. You can even help locate each other’s missing devices.

See also Share your location with your family.

With Family Sharing, it's easy to share your location with family members in Find My Friends or the Messages app. You can even help family members locate their missing devices in Find My iPhone.

As KiltedTim mentioned, for Family Sharing group members you can also see all their devices signed into their iCloud account (provided they have permitted this). These are visible in the Devices tab in Find My.

They can't. Your location is shared from a single device.

If you're a member of a family sharing group, that's a little different. In family sharing, if you share your location (which you are not required to do), the location of all of your devices can be seen.