Understanding the use of TWO routers

I visited a friend who is using two routers.
He has a Plusnet Router and connection (not ADSL), and this is connected by ethernet to a Vigor 2850 which he uses to administer a few computers in a local charity.
He thought of possibly using a type of home remote access so he can maintain settings and deal with problems from his laptop.

However we were both unclear of the best method.
The initial Plusnet router is on a 192.168.0.* subnet, whilst the Vigor which is fed by the ethernet cable is on a 192.168.7.* subnet.
We think this means that remote access to the Vigor and it's subnet is not possible, because the initial Plusnet router is working on a different subnet.

Is this going to be the case, or is there any workaround so he can access either router or subnet?

The first router on the DSL line (the Plusnet one) needs to either be in bridge mode (probably difficult) or at least have port forwards/DMZ to the Vigor in order that any incoming VPN connections get through to the Vigor 2850.

admin wrote: The first router on the DSL line (the Plusnet one) needs to either be in bridge mode (probably difficult) or at least have port forwards/DMZ to the Vigor in order that any incoming VPN connections get through to the Vigor 2850.

Thank you Admin

I would of thought the best and easiest way to do this would be to take out the plus net router altogether and setup and use the vigor router only, the plus net router is not needed