PPPoE and NAT are compatible.
I'm not sure what do you mean "two-way NAT"?
If you mean PAT, it is one thing,
if you mean two way dinamic NAT it is different.
For practical purposes, consider the PPPoE only as a protocol
for obtaining the IP address. As soon as TCP/IP stack is in place,
all ports ot TCP are supposedely open, so you should not have NAT problems.
I'd suggest to refer to CCO with PAT/NAT keywords.
Best,
Plamen