As far as I know, Interact is a keybind but is also a protected fuction.
As such, you can keybind to it, but cannot put it into a macro or script.
I could be wrong, but that's what others have posted regarding it.

You don't actually need to change to target the main, and then assist the main, and then click interact.

I have switched to a Target=TargetTarget system for my assist.
Use whatever assist method works as far as targeting goes.

The main selects something to die (or a Flight master).
The slaves use their assist of choice, if your Tilde key is follow the main and then assist the main, you're done.

Once the slaves are on the master's chosen target, click interact.