"How many people are there on the beach?"
Translation:Hvor mange personer er det på stranden?
Just a Norwegian passing by here. While "Hvor mange personer er det på stranden?" is gramatically correct and all, we do not really use "personer" unless we want to know the exact number. A more commonly used word instead of "personer" would be "folk". As in "hvor mange folk er det på standen?". Another also commonly used way, is to just drop personer/folk, and just ask "hvor mange er det på stranden"?. The latter is probably the most commonly used way. Hope this was helpful.
No, as we cannot assume from the English sentence that the people are actually lying on the beach. They could be running around, playing in the water, building sand castles, etc. :)