Spaying them both won't help, the dogs I have had problems with are both spayed, it has very little effect, infact they were probably worse afterwards.
There is an old saying, dogs fight for breeding rights, bitches fight for breathing rights..
I've found bitches that usually start to fight it turns out to be a lifelong problem, these dogs are sisters, and both terriers and one will probably end up killing the other. Problem is they are both the same age and have similar status therefore one will compete with the other to become "top dog".
It is impossible to get bitches to get along with each other once they start fighting and I can 100% guarantee spaying won't help, it don't have the same effect as it does with male dogs and even in some cases, failure can still be high with the males, my aunts male dogs fight even though both have been "chopped" and I dismiss that it's not because she's not in control of her dogs, most responsible people are, it's nothing to do with rank, her boys are behaved beautifully they just hate the sight of one another!
Crating them isn't a longterm solution, it isn't fair on either of them, I think you need to think if you can live like this with your dogs? With a dog of their size it's possible but human error needs to be taken into account and how you can manage this.
Other than getting a APDT reputable behaviourist in, I don't know what else to suggest but I doubt the quick fix solutions you are looking for here, isn't going to happen
You can find your nearest behaviourist here
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Unfortunately we went down that route with our dogs, it didn't work we had to resort to other methods.