David you keep your feedback when you change id's. You can just click on their "zeros" to find out when they registered and...if you are worried(if this is an expensive item),you could email them to make sure that they are both legit.
I know that when I first started on eBay I would always email a seller to let them know that I was legit but not everyone does so.
Remember that we all started out with a "zero" on eBay at one time.
If you want to remove their bids you can always go to the bidder management page and remove them and block them as well from ever bidding again on your items.
Up to you....give them a chance or nuke them.
Good luck