i need ADVICE,please

a friend of mine has this problem,and i just realized that im in the same boat,here's the situation
he has 4 females of 4 defferent breeds and types,all are almost the same age,he just got himself a male to breed to ONLY one of these females,then realized or remembered that the other three females are going to be in heat in some time as well,like his fourth female that he wants to breed
now all dogs live in the same house,what is he to do when any of the females go on heat?how to prevent the male from getting stressed?if to take the male out of the house,this could mean that the male would be out most of the year,and he cant do that
how far the heated female should be kept away from the males kennel,in order to prevent stress?is there anything to be done to help the male ?any advice is deeply apreciated
thnx