The tiger barbs need to be kept in groups as they can be aggressive, they should be in groups of at least 5 to disperse their aggression. One will always be boss and beat on the others on and off, if their is only one other then that one is getting the full blast of theothers aggression, when their is more of them, he spreads the beatings out between them in larger groups they are also happier.
The mollies could be mating? (not sure about that though). Have you checked the water quality lately? I often find when my fish are behaving oddly, something is going on in the water that I haven't noticed.
I have also just noticed you have one clown loach, they are serious shoaling fish and need the company of others, you should have at least 3. Also neons are shoaling fish and having 2 in one tank is unfair, maybe put then in with the other 5, or get some more to put in with them. (though I saw in another post you were having problems - maybe from over crowding). Just though I'd mention these things, as I'm sure you want your fishes to be happy and healthy, and I remembered when I started nobody told me, and when I found out I had already lost some fish and I was very upset.
Good luck, hope it helps.
