[Justin]

Thanks for the advise. Although the old one comes from a rescue center with well written checkup docs, I will get him to a vet and see what they say.

For aggression problem, it got better. As you said, the young one got tired of guarding old guy and now chasing other younger ones. Occasionally he checks up the old guy, but the old guy is now really relaxed and doesn't care it at all! He weighs more than five times anyway.

Young ones are now practicing a new move other than mounting. Its like they lower their hip to the ground, slowly shakes hip from side to side, and moves forward in slow motion. 5 weeks old ones do that sometimes when they approach the 9 weeks one. He doesn't tolerate that rude behaver and chase them away immediately because he is the only one who should do it. But they comes back after a while to do it again. *sigh*

And guess what my 5 year daughter told her mom last night. "Mommy, their p**** become long and short"