Let me take a guess without having the devices in front of me: I think the problem might be that your routers need to be on two different subnets. If you want to use cascaded routers you should leave the Linksys configured as your wife's employer left it, because you already know that works. Change YOUR router to a different subnet.
For example, if your present subnet Id is 192.168.1.x change it to 192.168.2.x. If your inhouse machines are set for DHCP they shouldn't have to be touched, maybe only rebooted to pick up the new address.
Set your inhouse router's Gateway/NextHop to point to the Linksys (probably 192.168.1.1). Once you've made the changes PING each device in turn until you're sure you can get thru both devices. Once that's working try your VPN again.
Great advice from all hands. Although you don't hace to reboot to pick up a nnew net config or DHCP prodived address. Just do an IPCONFIG /RELEASE followed by an IPCONFIG /RENEW from a command window.