Lance and Pidge sleeping in the same bed because they are used to having there siblings around at home and miss them. Since they are such good friends they consider each other as family.
Option 1: when Matt comes on the ship Pidge spends the whole time with him, but when it’s night asks lance if he still wants to sleep together.
Option 2: Pidge is to excited about Matt and doesn’t think about Lance. Keith sees that he is kinda sad and lonely so he says that he can sleep with him.