You don't give very much detail in your post - but if a 4 and 6 yr old are behaving badly it is their Dad's job to correct them. How long has this problem existed; how bad is it?  

Sit down with your DH and set ground rules for all the kids, polite and civil is expected at all times. Come up with an appropriate punishment. 

Nip it in the bud now or else it will only get worse.  Luckily they are very young, so a stern talking too followed up by a list of consequences if it continues, should do the trick. 

You tell them to cut the shit just as you would with anyone at your house.