Can PPTP VPN be made to go both ways?

pptp vpn is a old client server base vpn and it is not save.

for network to network vpn use ipsec vpn.

PPTP is a point to point VPN connecting only the originating client to the remote network.

Only the client gets an ip on the remote LAn or a special ip on the remote side that is granted rights to access the remore lan.
Only the client is directly accessible if routing is properly configured.

Device to device IPSec VPN will achieve what you are after.
Openvpn has the site to site VPN capability.

You want a site to site IPSec VPN, which is more ideally done at the router level. Arnold has best explained out why you cannot use PPTP.

Now that said, *could* you do a site to site with Windows Server? Yes. Would I recommend it? No.

The good old days approach (when PPTP was really used for VPN) has been to set up two RRAS servers, each one acting as a client for one and server for the other direction, using two different connections. Each client had to initiate his own connection.

So with your config it is not possible to do so, even if PPTP would still be acceptable.

To throw in another alternative: SoftEther. Though I prefer OpenVPN.

Why not get 2 firewalls/routers and setup an ipsec site to site vnpn.
then you have a solid solution that will work perfect.