Hey Mike! How are you doing!? (PS I'm a 'she'

)
Teog,
Your brittlestars are not likely to be exchanging anything. For one, the genital openings are both on the oral surface...so unless they are kissing mouth to mouth, there is not much going on. There are certainly species that do this, but not likely those in the hobby. Here is a shot of such a case (the male is smaller and is attached to the female):
Most brittlestars are broadcast spawners, releasing eggs and sperm into the water column. Fertilization is external; the larvae are extremely delicate and would not survive in our tanks. Also, various environmental cues are typically required to encourage spawning. Researchers often have to go to some extremes to encourage spawning in brittlestars (unlike sea urchins which seem to spawn all the time!).
There are exceptions, and they are found in our tanks. The tiny white
Amphipholis is quite common in tanks and is a self fertilizing hermaphrodite that broods its young. The striped species often reproduces through asexual splitting- fission (it typically has 6 arms).
Now what are your guys doing? Probably nothing out of the ordinary. In the wild, brittlestars often exist in high density aggregations. Some species, like our large shallow water tropical guys, coexist under rocks and coral heads. Some reports give densities as high as 30 individuals per sq meter!! However, if space or resources are limited, there may be some competition or aggression. This is usually not a problem in our tanks because the system can't sustain a wild bioload. In a low density situation, where resources are not limiting, they may be quite tolerant of each other. I have 5 large brittles in a 15g (lots of LR!!!) and they seem to tolerate each other just fine because each has a spot and they are individually fed. Sometimes they will hang out in the same area, but I haven't really seen any problems except during feeding. Then each one just wants to be first!

It is possible they are fighting, but usually one will go away as in most aggressive situations.
Sometimes it is just tough to know what is going on exactly. So long as they don't hurt each other, I don't see any reason to worry.