The problem is that devices physically connected my router cannot ping Android nodes connected over VPN. This seems to be an Android issue. When I took my windows 7 laptop to a cafe, connected it to the cafe's network and connected to my home network over VPN, the ping worked both ways. Devices that were physically in my house could ping my windows laptop and my windows laptop could ping them.
I tried the same thing with my Nexus 5 and Nexus 10, both could not be pinged from inside the house (although my Nexus devices could ping devices inside the house).
I am using 4.4.2 KitKat on both my nexus devices and connecting using the built-in PPTP settings menus. Can anyone throw a suggestion my way?