molly diseases

My little brother bought a pair of Orange Mollies today, when I looked at them I saw tiny black dots on their body and fins. I've currently put them in a quarantine tank. I just wanted to know if my other fish will start having problems if I add these to my main aquarium.

I have a guppy/ molly colony. A few of my older fish looked like they got guppy wasting disease. They got skinny then eventualy stopped swimming and died. But their poop never turned white and stringy. All my younger/ smaller fish show no signs. I still have 2 fish looking skinny, they are...