Were Frank and Tonny brothers?

I have now watched this trilogy multiple times through. In order, out of order, with commentary and without. And I am still unclear about this point...

Something about the first film gave me the impression that they were brothers...In fact I think they called each other "brother" at one point. But that could be like to dudes callin' each other brother, right? Or was Frank, the debt that Smeden refers to early in Pusher II? And I also wondered about Tonny and his less than favorable comment on Frank's mother when they are in the car in I. Like it was his step-mother or someone Smeden would've talked crap about...Does any of this make sense...I realized I have begun to ramble...And I just want to know it they were brothers?

"Master your high or die under the staff!"