Only one Weapons Team upgrade card for Wave 7, if you don't count the Boarding Team (Weapons Team + Offensive Retrofit) as well. Caitken and Shollan will fill an interesting role on a Rebel ship.
Caitken and Shollan - Rebel - 6 points
While attacking, you may exhaust this card to reroll any number of dice of 1 color.
We can see a few things from this card. It is an exhaust, so you won't want to rely on it for multiple attacks. You won't even want to rely on it for multiple colors, as they can only reroll 1 color of dice. However, you do get to choose the number of dice that you will reroll, unlike with Veteran Gunners, giving them the edge in that aspect at least.
On the other side of the coin from Veteran Gunners, Ordnance Experts let you reroll your black dice multiple times for cheaper (4 vs 6) making it the better purchase for black dice fleets. So this means Caitkin and Shollan are going to be best served on a ship with a single color of dice and preferably one big arc to attack from.
The MC75 which they come with ironically is not the best choice. With multiple colors (and not a ton of any single color) on each arc, and especially with Black dice being the biggest color dice on the Ordnance Cruiser, they will be effective, but less so than the alternatives. Unless you are doing some kind of Sato shenanigans, or going for Ackbar broadsides, then all bets are off.
The MC30 and Hammerheads suffer from the same problem. Too many colors and not enough of any single color to make the twins worthwhile, unless Ackbar shenanigans are your plan with a Scout MC30.
The Assault Frigate, especially with an Ackbar build, will have the twins compete with Gunnery Team for the Weapon Team slot. You'll lose out on the chance to shoot multiple targets, but the shot you take at one will be much better. Pretty much only Red dice that need to be rerolled lets you maximize the dice manipulation of the twins.
The MC80 Battle Cruiser and Star Cruiser likewise get a nod from the twins, if you are going for single big attacks and not multiple shots, and thus leaving your Gunnery Teams at home. By being one of the few ways the Rebels can get access to rerolls outside of Leading Shots, they can be put to use with the Star Cruiser to fish for critical hits or to augment the Battle Cruiser's long range attacks, letting it get in Cymoon 1 Refit type fire on the approach. With the new prevalence of Advanced Gunnery being taken as an objective, this even gives you the benefit of having a ship ready to take the boost!
That's it for the twins. We'll get back to the Rebel officers in our next upgrade article.