wireguard – what happens if several peers are using equal credentials / keys

Hello I have a question regarding to wireguard.

What happens if multiple clients (Peers) use the same credentials?

Example setup:

• I have a wireguard-server at home.
• I initiate a connection to the server with my smartphone and a minute later with my laptop. Both share the same Private and Public Keys and Wireguard-IP’s.

Possible outcome

1. None of the clients will be able to access the server.
2. The client that joins last takes over the connection and kicks out the client that joined prior.
3. The server will be able to serve all clients simultaneous?