(1) Yes, both the husband and wife can offer salah in the same room in the same time but both of them should not stand side by side rather they should stand with some gap. There should be the gap of more than two steps.
(2) No, it is not bida’h rather it is mustahab.
(3) It is not lawful. It is haram.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband