My brother and I live in the same house hold (share the same internet connection/IP) and we have no issues, I think if you both are wanting to play STRAT you have to post somewhere to let the devs know that you have more than one person playing at the same house hold but I'm not 100% sure on that, I think I remember being told to post somewhere but really I'm not sure so hopefully someone else can clarify. I think you should both be fine playing cRPG though.
If you try to join the same server at the EXACT same time it will most likely freeze, at least it does that for us. We have to take turns entering servers, other than that absolutely no issues. (to further explain, yes we can both be on the same server at the same time but when trying to join at the exact same time we both freeze
)
Anyway hope I've been slightly helpful !