As a human, I feel that after dead my ancestral soul are bind with God. If so why can't I allow to hang their photos with the God's? Is it abnormal thing to do?
When I heard some current guru asking not to keep departed parents' images in one's house, I could not believe my ears! It is so unfortunate for someone preaching Hinduism to say such a thing.
To a ward, parents and forefathers are gods.In fact the glory of mother is greater than heaven and this is well known. I hope the following quitations will make it clear that keeping their images is in fact encouraged. One of the nitya-karms or daily duties prescribed is pitri-tarpana as pitri-yajna, ie offering sacred water to the departed parents daily.So one must remember his departed parents regularly.Images also remind them.
Those who worship parents as gods have no need to worship any other gods. This was told by Bhishma to Yudisthira (in Santi-parva,Bhishma-Yudisthira-samvada,Rajadharmanushashana prakarana,chapter 18.
Yudisthira asked Bhishma: O Bharata! Among the different branches of Dharma, which one do you think is the most followable?
Bhishma said:Worshipping parents and the elder ones is the best Dharma...They are the three Vedas, they are the three Agnis. Just by serving them, one can win over the three worlds.In fact, their glory is more than that of Agni. All works of the ward who neglects his/her parents are fruitless. No one is more sinner than him who does not look after his parents.
One's father is the Garhapatya Agni and mother is the Dakshina Agni.Guru is Avahaniya Agni.One who serves these three adores all Dharmas.All works of him is fruitless who does not serve his parents and Acharya.(Chapter 2,slokas 225-237).
Of all Gurus,the mother is the most worshipable. If parents are satisfied with the ward, all fruits of Dharma come to him or her automatically. So one must try his best to serve and satisfy them.(Uparibhaga, chapter 11).
In Vrihat-Dharma-purana, we get the Pitri-Stotra and Matri-Stotra for worshipping the parents.
The the Baudhayana Dharma Sutras say about the Pancha-Mahayajna (2.11.1-5):
The following are five great yajnas [as part of regular duties]-- sacrifice to gods, sacrifice to ancestors, food sacrifice to beings, sacrifice to humans, and sacrifice to the Veda.
Katyayana-Smriti also prescribes the same duties:
One should know, as great yajnas, those that are performed successively daily for the Deities, the Spirits, the' departed Manes, for God(Brahman) and for mankind.
To deliver religious instructions, is the Brahmayajna ; to offer watery oblations, is the Pitriyajna ; to offer oblations of clarified butter to the Fire, is the Devayajna ; to offer Valis (offerings)) is the Bhutayajna ; and to treat guests, is the Nriyajna. (2 & 3, chapter 13)
As father is god, grand-father is god's god. I think it is clear from my answer that any ancestor's photo can be kept. And tarpana is offered to all the departed family members, at least for three generations to seven generation.Brahmaa is respected as He is the grand-father (pitAmaha) of the world.
(Reference: Srestha Dharma,Sitaramdas Omkarnath, Omkarnath Rachanavali, Mahamilan Math,Vol 6,page 114-125).