To add to what phender mentioned... in my opinion, these do have the potential to be Onyx clowns. A couple of questions for you. 1) Did you purchase these as Onyx clowns, or Solomon Island clowns? If you purchased them from the reputable dealer, they may know the lineage. 2) Do you notice the black filling in, or has it stopped? The reason I ask is because the black could feasibly fill in between the second and third stripes, and then I would consider them Onyx.
I am personally not tied to the C-Quest lineage for an Onyx to be an Onyx --as long as it's got the large percentage of black between all stripes I would consider it to be an Onyx. I've seen quite a few wild percs from the Solomon Islands that have a lot of black, including the dorsal fins, and I would call them wild Onyx clowns. This is similar to how I see zoas/palys that come in as wild colonies but look like "named" zoas/palys. Darth Mauls and Radiant Tangerines come to mind.
Regardless, I think you've got a beautiful pair of clowns, and if they've stopped changing, you may have stumbled across something some folks -- myself included -- may find to be more attractive than your standard Onyx clown.