It has been said that Hindus and Sikhs are two separate religions. However the inter-mingling of both communities specially in Punjab is important to understand as to why the Sikhs chose to be part of India and not Pakistan. The eldest of the Hindu families became amritdhari Sikhs, the inter marriages between the communities was also symbolic of how close these two communities were specially in pre-Partition Punjab and this tradition continues till today.
My father and mother had a bent of mind towards Sikh religion. They knew the Sikh scriptures Sukhmani Sahib by heart. One of my father's uncles had become a kesdhari Sikh. He did not marry and became a granthi at a gurudwara in Meghiana, the capital of Jhang district. After that, most Bhatla families in Jhang were more inclined towards the Sikh religion. The Bhatla brotherhood had constructed a gurudwara at Kot Khan, even though there was not even a single Sikh family living there.
Family of Satinder Mullick built a Gurdwara in Bannu, NWFP in pre-Partition India. See their story here,
The conflict with Mughals specially during Aurengzeb's time created friction between Sikhs and Muslims. However in the earlier period of the Sikh religion, Baba Guru Nanak's key followers were Muslims such as Bhai Mardana. Refer to the video here where a Muslim cleric talks about Baba Guru Nanak.