Yes, you can expose jellyfin via a reverse proxy or through a vpn like tailscale to your friends.

Quality and speed depends on what client they use, what transcoding hardware is in the server and your internet speed. For most usecases, a newer Intel based CPU can do 5-8 streams at once without issue, so it will likely depend on your internet connection.

I have an Intel N100 based mini PC on a 1Gbit/s upload connection running Jellyfin that I share with some friends. Usually 2-3 streams at once and it handles it well. Most of my media is in H264/MP4 with AAC audio, so they rarely transcode.