Spanking is not a effective way of discipling children, in my opinion.  Sounds like your boyfriend has not control over his children, so until he learns how to control them effectively, I wouldn't step in especially by spanking.  Sounds like he wants you to do the dirty work, because he doesn't want to deal with it.  You both need to sit down and figure out a constent plan that wil work amongst all the children.  I wounld not tolerate these kids screaming and behaving out of control, but it need to start with you boyfriend.   I believe if you are caring for his kids while he is at work then you need to let them know what is acceptable behavior in your house and let them know you will not tolerate this behavior.  Disciplining them doesn't have to be spanking them to get them to listen.  This usually causes children to be afraid, and untrusting of the parents.  You want children to respect you, then you have to give them respect.  You won't earn respect by a child by hitting them as a form of punishment.  There are better ways than that.

I know how yo fill about that i was there and no i dont spank his kid that way there cant be any leagal actions taken by there kids mother and so they have nothing to say aginst me as a mother what i do is i ground, take things that they like away , friends cant come over , they cant go to friends, and if you have a problem with home work dont let them up from ttable till its done ,and no electronics your kids are young i use to have a friday box if they fought over something or hit someone with something i took it away for a week and they didnt get it back. i hope some of these things help you with some of what is going on but dont give up there kids and they will test you to see what you let them get away with they will even though there mom up at you i just say ill tell her for you or we can tell her together and then i do let her know cause they will play both parents as much as they can i have been there if i had to do it all over agin i would cause i love each and evry one of them very much and i wont give up i know you will get fustrated i did and still do at times but you have to stick with a methiod that best works for you and the kids and some thing that if it dont work out with the both of you your man or there bilogical mother  cant say anything. its not worth lossing your own kids over i do time out to when they are grounded they are not aloud out side to play. if that stuff dont work give them chores to do around the house it not going to hurt them it just may hurt there fillings when i punished the kids i felt so bad for it but i cant give in then they know how to get there way . well nice talking to you by