My advice is, "Go for it!" There should be plenty of room in your 60-gallon aquarium for a couple of more pairs of seahorses without causing any undue stress for your resident kudas. Mustangs, Sunbursts and kudas all have comparable aquarium requirements and should get along splendidly together.
Go ahead and order the Deluxe Seahorse Special right now so you don’t miss out, but when you’ve choose your requested delivery date on the online order form, make it a couple of weeks from now to assure that your kuda can deliver his brood in peace before the new seahorses arrive. I can foresee no problems with the arrangement you propose.
In the meantime, get a nursery tank set up for your kuda fry.
Best of luck with your seahorses, Teresa!