Will my deadfather and dead grandmum get the reward of prayers and alms given on their behalf,though they died as non muslim?If not what can be done on their behaif.

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.

If it is confirmed that a particular person died on disbelief or while associating partners to Allaah without having repented from it, then it is not permissible to seek forgiveness for him or supplicate for him/her after his/her death. Allaah Says (what means): {It is not for the Prophet [] and those who have believed to ask forgiveness for the polytheists, even if they were relative, after it has become clear to them that they are companions of Hellfire.}[Quran 9:113] Besides, the Prophet said: "By Him in Whose Hand my soul is, there is no Jew or Christian of this community (of people from the time of the Prophet, sallallaahu ‘alayhi wa sallam, until the Day of Judgment) who hears about me and then dies without believing in what I was sent with, except that he will be amongst the people of Hellfire.” [Muslim]

Hence, if any person does a good deed while intending the reward for a dead non-Muslim, this will not benefit the dead non-Muslim in any case. Allaah Says (what means): {And We will approach [i.e. regard] what they have done of deeds and make them as dust dispersed.}[Quran 25:23]

If they do not benefit from a deed which they did by themselves due to their disbelief, then it is more appropriate that they will not benefit from the deeds gifted to them by others.

Moreover, there is nothing to be done for whoever dies on disbelief. You have a good example in the Prophets of Allaah. Ebraaheem (Abraham) refrained from seeking forgiveness for his father when the latter died as a non-Muslim, and Allaah forbade the Prophet from seeking forgiveness for his mother. Allaah is the All-Wise and He does what He wishes. He knows better where to put His Grace and Mercy, so you should not grief for that and you should let the matter to Allaah.  

Allaah Knows best.