I have read some of the answers on your web site related to the requirements of a valid baptism. You have mentioned a confession of your belief that Jesus Christ is the Son of God being required, and in accordance with 1 Timothy 6:12, that confession should be made before "many witnesses". My question is what would be your interpretation of "many witnesses"? The Bible says when "two or three have been gathered in my name, there I am with them" (Matthew 18:20). However, this is not said in context of a confession before baptism.
When Philip baptized the eunuch in Acts 8, were they by themselves or were there others present? The context would seem to indicate it was just Philip and the eunuch although we cannot speculate whether that was the case or not. There may have been others present but the text may not have recorded such. I know of people who have been baptized outside of a public worship assembly. There may have only been the person baptizing them present or maybe one or two other people there. Would you consider their baptism to be valid if this was the case?
In the case of the eunuch, he was sitting in a chariot reading (Acts 8:28). Later he commands the chariot to stop (Acts 8:38). This implies that there is at least one other person driving the chariot. But reason would tell us that a high court official traveling such a long journey would probably be going with a larger group.
It takes two or three to serve as a witness. "By the mouth of two or three witnesses every word shall be established" (II Corinthians 13:1). Even if we take the minimum, Philip and the chariot driver would make two witnesses to the eunuch's confession.