Can they offer the funeral prayer over one who did not pray for fear of fitnah that may result if they do not do it?
Question

                There is a village in which most of the inhabitants do not pray, but they adhere to some Islamic customs. There may be among them some who are kaafirs. We are a group who are religiously-committed and we are calling them to Allaah, and we have hopes that they will be guided. We only offer the funeral prayer for those who pray, but this causes fitnah if we do not offer the prayer for those who do not pray. 

Is it permissible to offer the funeral prayer for all people for the sake of da’wah?.
Praise be to Allah.
    The ruling on offering the funeral prayer 
    for one who did not pray is based on the difference of opinion among the 
    scholars as to whether he is a Muslim who is a sinner or a kaafir. The 
    apparent meaning of the texts and the consensus of the Sahaabah (may Allaah 
    be pleased with them) is that the one who does not pray is a kaafir in the 
    sense of major kufr. This has been discussed in the answer to question no.
    10061. In the answer to question 
    no. 70278 we stated that if a 
    person does not pray, we cannot eat meat slaughtered by him. In the answer 
    to question no. 37820 and
    49698 we stated that if a person 
    does not pray, no good deeds, zakaah, fasting, Hajj or anything will be 
    accepted from him. In the answer to question no.
    7864 we stated that the Muslims 
    should have their own graveyards, in which no one else should be buried, and 
    the one who does not pray and dies when he is not praying should not be 
    buried in the Muslim graveyard. 

    At the same time, we cannot deny that there 
    is another scholarly opinion on this issue, and there is nothing wrong with 
    the one who adopts it and believes in it. 

    If you think that the one who does not pray 
    is a kaafir, then do not offer the funeral prayer for one who died when he 
    was not praying, and put up with any trouble that may be caused to you by 
    the foolish. 

    If you do not think that the one who does 
    not pray is a kaafir, then there is nothing wrong with you offering the 
    funeral prayer for one who died when he was not praying, although it is 
    better not to offer the prayer for him, as a punishment to him and as a 
    deterrent to others from this major sin. Perhaps by not offering the funeral 
    prayer for him and others like him, you will motivate people to establish 
    regular prayer. 

    And Allaah knows best.