I took Caney to the beach once a few years ago --
best time of her life!!
The sand probably won't bother them at all. For obvious reasons though you'll want to rinse them off after they are done playing at the beach... to get the salt water and sand off of them.
They can potentially get sunburned, but it's really just the white parts that you have to worry about... for example I see that both your babies have white markings on the bridge of their noses... the hair there is very thin already, so that in combination with lack of pigment makes that area quite susceptible to sunburn. (Be thankful you don't have an ALL white dog in this case

:D)
Don't let them drink from the ocean -- it will make them sick! So make sure to bring water bottles and offer it to them very quickly if you catch them trying to drink the salt water.
Have fun and post pictures!! :D