It would take quite a bit more than two or three 10 kt devices to do that. Water is extremely heavy, and a lot of the water around a nuclear burst is just vaporized, not lifted and dropped.
For reference, the Crossroads Baker shot in 1946 involved a 20kt device (identical to Trinity and Nagasaki) exploded 80 ft deep in Bikini lagoon. The resulting wave swamped some of the target ships in the lagoon, and the reflected concussion blew the bottom out of a (target) aircraft carrier. However, the surrounding atoll was not at all wiped out by the tsunami. (AFAIK, it didn't do any appreciable damage on land.)
Detonate a 20 kt device or three at a depth of three hundred or more feet, perhaps one hundred miles apart. The swell created would devastate the coast in a very short time, and done at height of beach visitation time, the murder potential is astronomical. Don't make the mistake of under estimating the murderous intentions or potential of these demonspawn arising from Islam.
BTW, when I read about the damage to the atoll, it appeared pretty darn wrecked for habitation for years. It is now re-inhabited.