exactly what do first ones do?

Hunter Island FAQ
1

For example, I summon Zephys and everytime his turn comes up he just blinks on the screen for a second and the turn goes back to my next ark…

Also is there a list of each first ones moves or abilities somewhere?

2

They act as a temporary fourth monster. They either attack the enemies or they help your team out. 

You can see their abilities in the monsterpedia, way at the end at numbers 354 to 360.

3

Thanks…
Thanks…