Could you please guide me how to add srcnat to this subnet?Are they probably restricted to only accept connections from their own subnet? I've seen this a couple of times before.
Try adding a srcnat rule into this subnet.
Yes the DVRs are having IP 192.168.1.100 and default gateway 192.168.1.1 but still I can't ping them from my laptop 192.168.2.50Right.
Make sure the DVRs have that IP address (the one you additionally assigned to your router) as default gateway.