There is no magical way to talk to npc's although there might be I just don't know what it is, if someone else knows that would be amazing. Currently I just talk on my main grab the quest and share it. Turning in takes a bit of time sometimes.

The followers can target the main character and you can hit a hostile spell and it will automatically assist whatever the main is targeting. Works extremely well and is fast to update. Literally switching targets all activity is instantly on the new one.
Melee works the same way, there is a decent range for the melee hit box. If you are tanking a monster your followers are usually within range to swing. They also auto face whatever they are assist attacking.