Hey, lady! I wasn't trying to fob you off with a couple of books or minimize your problems. I know how hard it can be.
You said: WILL THE FIGHTING EVER STOP? I AM SO STRESSED OUT AND WORN OUT OVER THIS. NOTHING STOPS IT, UNLESS I PHYSICALLY PUT ONE IN A ROOM FOR A GIVEN PERIOD OF TIME. THEY ARE DRAWN TO EACHOTHER LIKE MAGNETS!
Just what mine would do. Yours are 7 and 4; mine are now 8 (almost 9) and 6, so the age differences are not too far off. It is better now than it was 2 years ago, so I do believe that there is hope. Will the fighting ever stop? Well... I doubt it will completely stop until one leaves home (that's how it was with me and my sister; we are good friends now), but relative peace can certainly be achieved.
The problems I identified when my cubs were about your cubs' ages were these. First, the younger one did not know what to do with himself and truly could not amuse himself for more than a very few minutes. So, he was looking for big sister or parents. Big sister was usually not interested in playing with him as he was nowhere near her level of capability and therefore not "fun" in her opinion. Second, the older one was extremely jealous of the younger one. He got a lot of time and attention. She also felt he got away with things she didn't at his age and this was true. She simply was more capable of understanding so I did expect more out of her.
As difficult child has gotten a little older, he can now play with his toys by himself a bit or watch a video for a while without looking for other humans. I have used the books I referenced early to talk with easy child about why she and her brother are treated differently. She is a smart girl and does see that what works with her doesn't work with him; she also sees that she gets additional privileges and treats that he doesn't because she does cooperate more and can be trusted.
Two years ago, I did send them to their rooms a lot. Usually, it was not just one that was at fault. My sister (the easy child) used to like to provoke the difficult child (me) and watch me get in trouble because I'd lose it and start yelling or hitting. My easy child will do the same, so I am very mindful of this behavior. Young children have an acute sense of justice and are very upset when they are punished for something that is not entirely their fault while the other party goes free.
I try to encourage them to cooperate in a variety of ways. They like videos (of course!) so I will say, You two can watch a video if you both agree on it or We will buy a container of ice cream if you agree on the flavor. It is interesting to watch them figure this out. I used to have to help a bit to make sure the younger one's interests were supported. Sometimes they got nothing at all because they wouldn't work together well and neither liked that. They have also learned to do what I call the "Simba and Nala" thing in Lion King where they ask for something, put their heads together, and say "Pleeeeeeeease?". I say things like, Well, when you work together, it's hard for me to say No, and will do things for a combined "Please" that neither cub will get on his or her own.
When the problems get too much, I make a point to say that if they can't play nicely together, they can play by themselves in their rooms. I talk to each one and make each one say independently that they will work on getting along with the sibling better. Before releasing them back into the wild, I make sure that the original bone of contention is gone, if that's appropriate. For instance, easy child would do things like switch the video if difficult child was watching one and he'd become unglued. I figure that yes, he shouldn't have smacked her over it, but easy child was in the wrong and difficult child shouldn't lose his video for that. So he'll spend some time in his room to contemplate the concept that it's wrong to hit sister no matter what, but he does get his video back after. Not the case if they are both fighting over videos in the first place, if that makes sense to you.
I tell them regularly that they will value the sibling relationship someday, that there will only be one other person in the world who understands some of the things they are talking about. I tell easy child that she will want him to move her furniture someday so it pays to be nice to him now because she understands the concept of wanting something in the future; her brother doesn't even understand "tomorrow" particularly well in my opinion. I tell difficult child that easy child is his blood and is to be valued and protected, not harmed; this appeals to him because he wants to be the big, strong man.
So, first, time helped since they can both now anuse themselves independenly for a while. Second, strongly encouraging them to work together (yeah, some would call it bribery) helped them see each other as useful allies. Third, working with each one's individual motivators to see the other as something other than the enemy helped.
And as for me, well, anti-depressants are a marvelous thing. Prayer and meditation are also good. Haven't tried yoga yet, but I bet that would be a good tool for me, too.
Hope this was more useful than my first post. Good luck, lady.