You have had the cats for 4 years - is that correct? And this problem started 6 months after you got them - is that correct?
So this problem has existed for 3 1/2 years, if my math is correct.
Why did you wait so long to find a solution?
I also recommend you get all of them to the Vet as soon as possible. Get that female fixed - that alone might solve the problem. However, since this has been going on so long, it's probably just second nature to them now.
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