You would have to not only figure out how to get it to work but then, any router update or change and it's all this work again.

Do not sign up for such advanced cases.

Also, if all 3 DVRs are the same make, you as the network engineer have to see if they support changing the PORT numbers and how to run their apps.

Simply a very advanced setup that should never be seen in a consumer setting. This would be a business where they employ IT staff.