Translation:Christians, Muslims and Jews believe in one god.
Ignoring the... substantial theological debate in the comments... as far as sentence translation goes, would this sentence as presented here generally be interpreted as saying that each of these religions has one deity, or that all three of them have the same deity? From a strictly grammatical standpoint.
The first option.
For the same god, you'd use באותו אל. Possibly באלוהים, though it's more ambiguous.
This is a language learning course. Atleast i thought so. Suddenly it makes more sense to me why there are so many wars about religion in the world.