I have 3 ER7212PC, in 3 different sites. 

 I'll call them #1, #2 and #3.

I want all clients that connect to device #1, #2, #3, to route all internet traffic via device #3.

I have VPN set up between each routers and can see / access each local networks from any sites. 

1)

Now, I want to make sure that all clients connecting to device #1, #2, #3 ONLY use device #3's public internet access. So all traffic needs to be routed from device #1 and #2 via the VPN to device #3 i assume?

2)

Can I explicitly BLOCK internet traffic if the VPN to device #3 is down?

Thanks.