.... Does anyone know if linked reservations are given the same muster station?
Generally no. If fact, .... NO ! ! !. 
Usually those requesting connecting cabins don't care about Muster Stations. Since it's a challenge just to find adjoining/connecting staterooms, usually that is the last consideration , on the request list for pax.
Connecting Muster Stations is usually the last consideration, not only for DCL, but usually for pax too. Having different Musters, is easily overcome aboard, if necessary.
I'll admit a request for connecting Muster is a first. 
Yet, it proves you have done your research, that's for sure.
Asking for cabins in a specific category, then adjoining, then connecting, then veranda connecting, then a specific deck, then extended veranda, then away from any noise, then the same muster stations is rare.
That doesn't mean you can't figure it out using the threads here, if you need connecting Muster cabins.
DCL may also be able to help, if you need congruent muster stations, but I find it unlikely.
DCL will be no use, I guarantee.
These Muster Stations are assigned vertically throughout the vessel. IMO. That is a vertical component throughout the ship, so you may be able to extrapolate the existing data to generate the locales needed for your cabin assignments.
On our last sailing on the Magic, we had the same muster station as our kids and care provider even though they were a deck below us.
You were just lucky IMO. Or you had a great TA, who knows more than most.
And a cruise before that on a different line, we had different stations (despite being across the hall from one another) but they changed it so we could be together. Just wondering what yo expect - on the Fantasy this time.
DCL requests you book one adult in each room with a minor. If connecting/across hall allowances are made.
Book what you want. Then work it out aboard.
Most feel Muster station is the last thing they worry about, although it does play a role with kids.
Such as, you book two rooms with 1A1K in each, the rooms are connecting, yet they are in different Musters. It happens all the time.
You can book one room for the kids in an inside, then another, opposite the hall for the adults, in a veranda. And it is all good. DCL will work e=with you, Once Aboard.
Most prefer to place the focus on great cabin and locale.
The Fantasy Rocks. No worries.
Do you have some room #'s ? ? That may help us focus our responses.
