I have a 15y and a 17 yr old son and when my husb and I go out we leave them in charge of our 6 yr old daugh?

and 10 yr old son which are good kids and well its their bro and sister but now when my sister n law wants to come with us she wants me to leave my kids watching her kids 3 yr old and another 10 yr old and i gotta say when hey are together they can get out of hand, anyway I dont agree with leaving them all 4 here I feel that my sons are not so attentive and not their responsibility to be watching 2 more kids so we end up staying home, advice please