Are the transaction balances each equal to $0.00? In order to be moved to History, a transaction must have a zero balance, not just match some other transactions that, when combined, total to $0.00.

If they have $0.00 balances, then the Period End process should move them to History.

But that's not the end of the story! You won't be able to delete those Vendors even after the transactions are in History. You will have to clear the transactions from History first.

The Period End process also has a check-box that allows you to purge all transactions before a certain date (the date is determined by a setting on the Company Profile). Note that ALL transactions are cleared, not just for your 2 Vendors.

Knowing that, do you really want to get rid of the 2 Vendors knowing that the price is the loss of your transaction History? If you rely on your Vendor history data at all, then you should probably live with keeping the 2 Vendors.