It's possible that your dalmatian molleys are chasing your male because they're establishing dominance. Are you sure of the genders as well? I'm not questioning you, but it could also be that a male is possibly chasing your female.
As for telling if she's pregnant, is there any possible way of taking less blurry pictures? I'm just curious to see if there could be any more details. Has she been acting any differently, trying to hide away from the other ones? Has she been less active?