My friend has a minecraft realm, she can play on it with my wife just fine. When I join from home I get force kicked by host exception, as the game thinks our router IP is DDOS attacking her realm when I try to join. I can play on it just fine if my wife disconnects, or if I go to a friends house, though with covid that's not really viable. The only direct solution on my end would be to use a VPN to alter my IP. On the Coding end however you could lax the DDOS protection a bit to allow at least 3 people to join a realm from the same house. The only other alternative would be to copy her realms files, and just re-host her server myself. Which honestly seems like the fastest solution, especially given this has been a problem since at least 2018 from what I read in the forums already.