Is it permissible for the Imam to combine the Adhan, Iqamah, and Imamat, or the Iqamah and Imamat, and what is the ruling on the prayer of the congregant at that time?

It is permissible for the Imam to undertake the Adhan (call to prayer), the Iqama (second call to prayer), and the Imamate (leading the prayer). It is also permissible for him to undertake only the Adhan and the Imamate. Likewise, it is permissible to combine the Iqama and the Imamate. The prayer of the Imam and the congregants is valid in all these cases.