Multiple hardware firewalls on a network.

Current networks exist at each location and they have a firewall installed. I want to install a second firewall since we do not own the existing one. The primary function is to connect the main site with all the remote sites via point to point VPN tunnel and use our own Firewall/VPN. The main site has a T1 data line and the remote sites have DSL or Cable.

Is it possible to run firewalls in parallel on the T1 and DSL?
I there another solution to this project?