Concerns for Baby's Safety

I've had two year olds and newborns a time or two before, and it wasn't a problem then. This time I am truly a bit worried. For one, Justice (my two year old) is very jealous of anybody else getting too much Mommy attention. For instance, if Mark (the six year old) sits on my lap, Justice comes over, pushes him off and yells "MY MOMMY, MY SEAT!!"

For another thing, Justice really likes to bully his brothers around. I'm hoping that this is just to prove his might because he is so much smaller than the other two (6 and 8 yrs old). Maybe he won't feel the need to prove his might to a little baby. I don't know. He really likes to hit and throw things at Ross and Mark. He doesn't have this problem with other children in nursery (his own age), so that's a good sign. It is a daily occurrence that Mark cowers away from Justice's aggressions. Justice threw a heavy shoe, the kind with retractable wheels on the bottom, and hit Mark in the head the other day. Just now, I came in to find Mark lying on the couch with Justice jumping up and down on his chest. Argh, this is going to take "Constant Vigilance!"