If "mixed environment" only means that there are hosts running various OS's at both locations, it's fairly irrelevant.
Anyway, I am using OpenVPN for what appears to be a similar scenario--routing traffic between a relative's and my house. I don't have Internet traffic from one site being routed through the other, although the VPN certainly could be configured that way.
I will also echo the previous recommendation for PFSense, which I am using on one side of the VPN (running on a fairly inexpensive ALIX board). On the other side, I'm using an Ubiquiti EdgeRouter Lite. I can heartily recommend either one, but particularly the EdgeRouter which can't be beat for its ~$100 street price.