In بُيُوتُ مُسْلِمِي الْمَدِينَةِ, 'the houses of the Muslims of Madinah,' what was the original form of مُسْلِمِي, and what change occurred?

It was مُسْلِمِينَ; because it became a muḍāf, its final nūn was removed, producing مُسْلِمِي
It was مُسْلِمُونَ, and a ḍammah was added
It was مُسْلِمَانِ