Yellowhead gobbie and Yashia Gobie

Both of those should eat mysis and that is a mansion size tank for those 2 fish.. you can have 10 of those size gobies in that tank if you wanted. You may want to get some frozen Cyclops and maybe Arctipods as well for the yasha, I know they eat both of those as well and they are smaller than mysis.

I know this goes against the proper advice, but personally I would just slowly acclimate them in a bucket for 1/2 hour or so and then put them in your display tank. Those 2 fish are not known to be real disease carriers (although it is alway possible). Fish I think really need QT are larger fish, especially Tangs and Angels, but gobies I have had much better luck putting them in my tank then if I try to QT them first. JMO.. like I said, I know it goes against proper advice so take it for what its worth.

Same thing.. actually more so with the jawfish. They seem to really stress out in QT tanks if they dont have a place to burrow and proper substrate to build their den. Yashas are also a very delicate fish. I lost 2 in QT and 3rd try I just threw it in my tank and it survived. At 3 months old your tank should be fine for gobies and jawfish to sift through.. that is plenty of time for the sandbed to get established.