These days many Srivaishnava worship other demigods and accept them as their kula deivam. When we tell them that we as Srivaishnava should worship Sriman Narayana alone, they say that we will beget sin if we do not worship other Gods and ridicule us. How to reform them?

It is enough if we worship Sriman Narayana alone; let them ridicule. To explain it in a worldly manner, a prime minister has the authority to oversee or change all the ministries; similarly, Sriman Narayana is the supreme God who appoints all the demigods to do their roles. When the prime minister is close to us and is willing to do our bid why should we seek other ministers? We need absolute faith in our Lord Sriman Narayana and need not resort to other Gods and no sin will be accrued as a result.