48. Those of them who are in the heaven of the Mohammedans have only one wife, having rejected more. For there is a Mohammedan heaven distinct from the Christian heaven. But those who eventually, as many do, acknowledge the Lord as one with the Father are separated and are in heavens which communicate with the Christian heavens; and they have conjugial love.

Darkness" is a state without light. "Light" is truth from the Lord, so "darkness" represents a state where truth is lacking. Here's a cogent passage from Arcana Coelestia: "The person who has yet to be regenerated is called 'a void and an empty earth', and also 'ground', in which no good or truth at all has been sown - 'void' where there is no good, and 'empty' where there is no truth. Consequently there is 'thick darkness', or stupidity and lack of knowledge about anything that has to do with faith in the Lord and so anything that has to do with spiritual and celestial life. (Arcana Coelestia 17)