Pretty hard to scare a hawk since shooting it is against the law, here anyway. You may be able to frustrate it but once it knows a meal is there they will be back. Make sure there are hiding places your chickens can run too, staying out with them helps, if you can, buy a guard dog, hang cd's, play a radio. I have heard all of these but not sure how well they help. I have been fortunate and haven't had any problems. I know a lot of people hate crows but I feed the ones living here to keep them here and they chase the hawks away. Every other day the hawks try to come back but the crows are right there doing what I want them to do. Most everyone in my area has chickens so the crows are plentiful. I'm sure someone else who has had problems with hawks can give you better advice. Wish you luck.
At this time of year I have frequently seen redtails hunting as a pair with the seasons offspring. The 4 may just be a family that think they have located a chicken buffet. Supervised free ranging and a covered pen are your best solutions to the problem.