I have a question about John 1:19-28. I noticed that the priests and Levites asked John the Baptist whether he is the Messiah, Elijah or the Prophet, multiple times. Additionally, they asked John why he would baptize if he were not the Messiah, Elijah or the Prophet. I was curious to see if they were interested in finding out who John was, or if baptism at that time was facilitated by people in high positions.

I don’t think there is enough information available to provide a full answer to your question. People were naturally intrigued by the figure of John the Baptist. Some also resented him, as (like Elijah) he did not hesitate to challenge the status quo.

Have you read the N.T. Chapter Study on John 1? While I am unaware of others practicing baptism outside of John’s movement (until Christian baptism became available, at Pentecost, Acts 2), the widespread practice of self-immersion in a miqveh is well known. See also Q&A 0522. The most devout (including priests) immersed themselves daily, and the rich often had private immersion pools in their homes.