-First thing is to pull your free credit report and see who is claiming what amounts are due.
-Second. There are different types of collections agencies. Primarily in house, third party and zombie collectors. If you are still in house with Capital One I would try to work with them first.
Capitol One wants their money. You can try to negotiate it but there is no standard discount amount they will settle for. Start with a number that you can write a good check for today and see if they take it. If they insist on all of it ask to freeze the balance with no further interest and make payments.
As for the other debts.... if you have not been contacted for 3 months it is possible that the debt was written off (that is why you check your credit report) and the primary company will not contact you anymore.
It is also possible that your debt is being sold to another company for a discount.
You can definitely negotiate with them as they will try to get the full face value but don't have as much at risk.
Good Luck.