I'll need to take a look into the site to site VPN capabilities, but I'm a pretty big fan of Ubiquiti's Unifi line in the advanced home networking/small business space.
I'd suggest looking at a Unifi USG as router at each house ($100-120 ea), then run the controller software in AWS, Azure, or other cloud service to let you remote admin both installs. To be clear, this is a Router only and does not have a wireless access point integrated. I've seen much better stability since switching to a separate router and WAPs on my home network.
https://www.ubnt.com/unifi-routing/usg/
https://help.ubnt.com/hc/en-us/artic...n-Web-Services
If you're going down this road, I'd also take a look at deploying Unifi APs. You would be able to manage those through the same controller software. If you're looking to pinch pennies, you can likely reconfigure their current router/wap combo to act as a WAP only.