I sometimes play in a net cafe with some friends so we all log at the same time.
And mi building have free wifi so mi brother and neighbours log from the same IP.
Is there any problem if some of us have main char+buffer?.
Since you put that weird rule of "2 ppl playing in the same house".
There's no need to ask, if you play with another person don't worry about rules. But if you are asking is because you're planning to multibox and then make others think that it's your little brother ;) ;)
If you're playing from the same IP, but you're only using 2 characters in the field each, then it's fine.
If you have 3 characters following your character, it's not fine. And it's very very very easy to see when someone is multiboxing several characters.