pf.conf
Host "foo"

ext_if="sis0"
int_if="sis1"
set skip on { lo $int_if enc0 }

nat on $ext_if from !($ext_if) -> ($ext_if:0)

block in
pass quick on $ext_if from 192.168.10.2
pass out

Host "bar"

ext_if="sis0"
int_if="sis1"
set skip on { lo $int_if enc0 }

nat on $ext_if from !($ext_if) -> ($ext_if:0)

block in
pass quick on $ext_if from 192.168.10.1
pass out