I need units to be next to each other in order for them to do a combination attack right?
So have a Twin Unit next to each other, and also have another 2 units next to the twin unit to get a big team attack with 4?
What does the text say when I choose a unit and friendlies will have text over them with a 1 or 2?
To get an 4 attacks in one go, the units you park next to the one attacking needs to have the Support Attack Skill. 援護攻撃 is what it looks like. When you hover, the Red one indicates how many times they can support attack, The Blue one indicates how many times they can Support Defend i.e. take damage for a unit.
Team-Up attacks, are initiated by whatever unit you use, and you only need their partner unit parked next to them, either directly or diagonally. They don't need them to support attack at all, just be near each other.
If you combine the support attacks + team up attacks, you can get a giant robot festival.
For reference, this is what it looks like when you get 4 units doing their team-up attacks in a big setup. This is from the first game on the PS2.
http://www.youtube.com/watch?v=IfLsea2PVzc&feature=g-crec-u