Is it permissible for a Muslim to initiate greeting all residents of a building, including non-Muslims, knowing that it is not permissible to initiate greeting disbelievers?

It is not permissible to initiate a greeting of peace (salaam) to disbelievers according to the majority of scholars, and this is the correct madhhab (school of thought). If Muslims and disbelievers are gathered in a majlis (assembly), it is recommended to give the greeting with the intention for the Muslims, as the Prophet, peace and blessings be upon him, did when he passed by an assembly that contained a mix of Muslims, polytheists, and Jews, and he greeted them.