How to add a team from team builder to multi

Correct, the person setting up the dynasty has to have downloaded them and has to add them in when creating the dynasty. Then when you join, you will have that team there to select. You cannot add them after it's been created.

And just to make sure you're aware when doing so, you have the option to make your roster the team who your teambuilder team replaces. If you use a preset roster like "cupcake" and another of your friends does the same, you will have identical rosters with identical player names and attributes. 

Additionally, you will inherit the location of the team you replace. So if you're saying your team is in Alaska but you replace Georgia Southern, your proximity to home is going to be based on Georgia Southern's location.

@woodwardm28thanks for this, another stupid question...how does the individual who is setting up the dynasty grab the teams to add? I tried to share my team with him but i don't see that option. Where does one search or how do you search to gather the teams? We are all on PS5 btw.