Can I consolidate charged-off accounts?

If the charged-off account has been sold to a collection agency, then you have to negotiate with them. Don't expect that the charged-off account will drop from your credit report after paying it off. Only the account status will be updated.

It is possible. However, this depends on how long the debt has been charged off. You might have to negotiate with the creditor a bit for that.

I have heard that such accounts stay on the credit report for 7 years. But, it is always good to make repayment as much as possible.

Did you talk to your creditors or collection agency? Did you get permission to pay off the debts?