ok lets say that my opponent is playing titans and they have started exhausting characters for roy harperthen they declare that they are going to use roy harpers ability, and in response i use a power to make him exhaust a character, would roy harper just be exhausted or what?

Same scenario except they have two characters that are not exhausted. i then force them to exhaust a character, then they use terra's ability, would they have to then exhaust roy harper or would i have to force them to exhaust another character?

Last question I force them to exhaust a character, in response the use roy harper (again there only unexhausted character) could i then force them to exhaust a character all over again?

To tell you the truth, there is far too much going on in this question to give it an accurate answer.

Is the opponent exhausting all of his characters at once, or exhausting them and then resolving the ATK pumps one at a time?

How are you trying to force an exhaustion---an effect where you target the opponent, and they choose, like Puppet Master? Or an effect where you target a character to exhaust, like Mystical Paralysis? Or even something like Justice, Like Lightning, where you choose someone at resolution?

There's a great deal of precision involved in playing Titans, and often in defeating them, too. To help you understand a situation like this one better, it'll help if you can make us understand it, first.

they choose whom they exhaust, but i can do this as many times a turn as i want so it really doesnt matter, but for the sake of posterity they choose whom they exhaust

Based on other threads, then, I'm going to guess that you want to use Erg with a Medallion of Power. He's got an activated power, though, so you need to be able to ready him each time that you send him back to the hidden area to use it.

The situation's description is still lacking tha important point of how the opponent goes about pumping Roy Harper, which changes a lot about the possible responses. But as a general foreword, remember that you can't interrupt your opponent's paying of a cost.

well
a) spoiled
and
b) drat others had that idea

although i dont think any one has had the thought of annelee and kayman, using the watchdong and longshot as your visible characters