This is in regards to Shakeel bin haneef, who claims to be Imam Mahdi and Jesus, peace be with him. His followers preach and try to convince others to believe in Shakeel.
1. Are the Shakeeliyans out of the fold of Islam?
2. Can we let them offer the prayer in our masjid?
3. Is marriage allowed with them? If someone is already married and their spouse starts to believe that Shakeel is Imam Mahdi and jesus, peace be upon him, is their marriage still valid then?
May Allaah reward you.

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad is His slave and Messenger.

Claiming Prophethood is disbelief in Allaah Almighty because it is denying what Allaah and His Messenger stated.

Allaah informed us in His Book that he had sealed Prophethood with Prophet Muhammad as Allaah says (what means): {Muhammad is not the father of [any] one of your men, but [he is] the Messenger of Allaah and the last of the prophets. And ever is Allaah, of all things, Knowing.} [Quran 33:40]

Moreover, Abu Hurayrah narrated that the Prophet said, “I have been given superiority over other Prophets in six respects … and the line of Prophets was sealed with me." [Muslim]

Also, the Prophet informed us that there would be impostors claiming Prophethood in this nation.

Thawbaan narrated that the Prophet said, “There will be thirty liars in my nation, all of them claiming to be a Prophet while I am the last Prophet and there is no Prophet after me.” [Ahmad and Abu Daawood]

Believing in whoever claims to be a Prophet is kufr (disbelief), but this ruling is general; i.e. it applies collectively to those who get this description. As regards declaring a specific person a disbeliever and applying the rulings of kufr on him, however, then there are Islamic terms and conditions for this. They were previously clarified in fataawa 87963 and 8106.

In such issues, one should take the case to distinguished scholars in that country and ask them about it as they are more aware of the circumstances there.

Allaah knows best.