Trigger/Spell Help

Hi i was wondering how if this is possible and how would i attemp to tackle this:

a) Have a unit follow another unit with a maximum distance they can be apart.

b) Have a unit follow follow a hero with a maximum distance they can be apart.

c) Make two heroes cann't be more the XX distance away from each other.

What i really want is c) but i have looked at WE but can't figure if it is possible or not. can anyone help?

Cheers
Archy

hm..i think i can help

Follow Unit
Events
Map initialization
Conditions
Actions
Unit Group - Order (Units in (Playable map area)) to Follow (First unit of group (Units within 600.00 of (Position of (Triggering unit))))

Q1 and Q2
Well i know how to detect it:

Events: Every 1.00 seconds of game time
Conditions: None
Actions: If (Distance between (Position of (Unit1)) and (Position of (Unit2))) Less than or equal to 500.00 then Your actions.

How to get the unit to come within range again is another problem.
Unit1 and Unit2 is Unit Variables. And the condition is a real comparision.

Q3: The same thing.