Hmmm...all just depends, I suppose.
Rose, in her younger years, would have attacked with no questions asked. She and Blackie did NOT tolerate any strange dog on their turf at all and they would back that up with their teeth. Now in her older age (and that she is a lot more used to use bringing home fosters), she would probably just posture and bark, but not attack - if the dog was being submissive/nonthreatening.
Chloe, it just depends on her mood. She would probably posture and growl and be a bitch, but if the dog didn't take offense to that she'd likely knock it off and become friends. If they did take offense to that, she'd attack.
Cynder would put her hackles up and investigate. Then if the dog left her alone and wasn't confrontational, she'd do the same. Otherwise, she snarks to be left alone.