As a professional musician there were plenty of times I would be playing w/ 3 or 4 bands so I could keep the income I needed to avoid a day gig. You could always use the other guy as a sub for when you want to schedule a gig on a date that the other bass player has a conflict with.
On the plus side, if this guy is gigging w/another band that could have the potential of opening a lot of jobs for you. Club owners like dealing w/people they know, so if he's in tight w/a couple of these owners they may book you sight-un-seen on the reputation of this bass player. Just something to think about.
BTW, I think it's pretty cool your dad is playing drums for your band.
Play w/people who inspire you and bring out the best in your playing. It's inevitable that a good bass player is gonna come w/some baggage, it's like dating a really hot chic, everybodys' gone want her and try there damnest to steal her away.
