Do I submit supporting documents for someone traveling with me who needs a visa?

One of my close relatives, an Indian citizen, is applying for a tourist visa to UK. I, my wife, and son are planning to travel with him. We are US citizens, so we do not need a visa. My relative is planning to put our names as people traveling with him. My relative is funding his part of the journey. So we are not sponsoring him or vice versa. We are traveling through the UK together, staying at the same hotels, etc.

The worry is that if my relative applied as one who is traveling alone, his application is likely to be rejected. In this case, the truth is that we are all traveling together, so we thought that mentioning this would add strength to his visa application.

Do I and my family need to submit any supporting documents? (If not, I would think anyone can write such things in their application.) I asked this question to the British High Commission in India, but their reply seemed to be auto-generated and did not have any useful information.

I would have thought that it would be useful to submit our passport details and possibly airline tickets and even bank information to convince the visa officer that we have the means to support ourselves. But that is just my hunch.