As Salaamu Alaykum wa Rahmatullahi Wa Barakaatuh 

There is an individual in the UK who grew up in a Sunni Muslim household, and attended local madrasa, and became Hafiz of Qur’an. Later, he went to University, and his aqeedah regarding Abu Bakr (RA) changed. He claims he believes in everything of Islam except he believes Abu Bakr was a genuine believer, and companion during  the life of the Prophet (SAW), but after the Prophet’s (SAW) demise, he become an apostate/murtad (astagfirullah), and subsequently did not die as a Sahabi, rather he died upon kufr.

So my questions are as follows:

1. In light of the Arabic texts from reliable sources, is the above person a Muslim, or has this element of his belief taken him out of the fold of Islam?
2. Is his nikah with his wife broken?
3. Will his Muslim children receive inheritance from him?
4. If he dies on this stance should we offer him salatul janaza?

A local Mufti claims that “the aforementioned individual is still a Muslim, because saying Abu Bakr (RA) died on kufr” doesn’t make him a kafir.

1. What is the ruling on such a Mufti? Is he on the creed of Ahlus Sunnah or is he deviated?
2. Although, he does not do takfir on siddique akbhar himself, does his insistence on declaring the above university student (in the scenario above) a Muslim effect his own Imaan in anyway?
3. Is it permissible to offer salah behind such a Mufti? 

Hazrat, please answer each question accordingly, and in full. iI it permissible I can share your answer to the confused invidiously, and to other people it might benefit?

Jazak’Allah!