Sikhism respects all religions and there beliefs. Remember Sikhism Speaks to people of no religion and Sikhism is not a religion it is a way of life. Sikhism has no rituals and there is no way to convert into Sikhism. A Sikh must follow the Guru teachings and cleanse the soul from the five thieves. Once the Sikh follows Sri Guru Granth Sahib then he/she can take amrit(holy water), which purifies the Sikh by the Gurus blessing and he/she becomes a part of the Khalsa panth. A true Sikh will not marry outside of Sikhism. This is because once the person is true to the Guru, there is no other than the Sri Guru Granth Sahib he/she has fallen in love with Sri Guru Granth Sahib. A husband or wife is a person you share the journey of life with and to do this in the best way the two should connect on a intelluctual level.