V.W.
Hi Tammi!
That's a tough one that I think we all struggle with. My kids (son 10yrs next month, daughter 7yrs in 2 weeks) get that way too. And often. But really, if I think about it, MOST of the time, they play together and get along quite well. It's just that we NOTICE more when they don't. (I know that's probably true at your house too, isn't it?) And all the experts say that when kids are "bad" they are trying to get attention, whatever it takes... I think part of it is just struggling to figure out how they "fit" into things: the family, their friends, the world. Particularly as close in age as yours are, maybe competition with each other is a constant factor. (Mine are not ALWAYS competitive, but introduce a third playmate into the mix and it is INSTANT).
Is it possible to spend one on one time with them separately? When one of mine has another activity (goes to a friend's house for the afternoon, or a birthday party, etc) I like to do something "special" with the other one- even if that "special" thing is just teaching them how to clean the bathroom, lol. Or let Dad take one to do something and I do something with the other one. They get to have sole attention for a bit without having to compete for it. (And then talk about what you did over dinner all together).
Another thing I find is that if I let my kids go somewhere together without us (the parents) they stick pretty close and enjoy each other. Let them go to their grandparents', or aunt's for a day or two or three... or even just swap them out with some family friends (you can offer to do the same with their kids if they have some).
When I let them do things on their own, they usually get along much better, especially if I stay way back and observe without being noticed observing. If I am visible or in earshot, they don't work things out, they tattle and complain to me constantly about the other. I have learned to ignore a lot. Usually their interest in "getting" the other one fades as fast as my interest in hearing about it...
I don't know if any of this will help you, but if you find a better way, let the rest of us in on it! LOL...
Oh, one other quick thing: I also have found that if I let them sit in front of the TV (even for a little while, but I'm guilty of long TV afternoons when I really need to get something done without worrying what they are up to) they get much more irritable... with each other and with me. When I don't let them watch, they have to become much more creative to stay entertained... and they usually figure something out together and get along.. at least until they get worn out or hungry!