Sandboxing by definition will require more than one NIC. His question was whether or not he needed a second NIC
on his Blueiris machine, and the answer to that is no. Normal implementation with respect to this scenario:
Cameras and server are all within the same VLAN on a separate switch. That switch is connected to one port on a router. Your other clients are connected to other switches (maybe all in the same second vlan, maybe as in my case into many vlans), which are connected to other ports on the router. The router has rules defined on it which specify what traffic is (or in the case of a sandbox - is not) permitted to travel between individual vlans.
Depending on the switch (I'm a Cisco guy, so that's what I know), you can also implement access lists to control traffic between vlans which are collocated on the same switch and thereby achieve the same sandbox within the confines of the switch itself, but in a simple home network setup like what you're discussing, it wouldn't be worth the effort.