***Speculating that the Apostles who previously followed John the Baptist had been baptized by him is no greater a leap than speculating that they might also have been baptized by Jesus.***
Why would a follower of John the Baptist need to be rebaptized?
John required repentance, works to prove it, and required those being baptized to believe on Jesus, the very things your church requires.
Acts 19:3-7
3 And he said to them, “Into what then were you baptized?” So they said, “Into John’s baptism.” 4 Then Paul said, “John indeed baptized with a baptism of repentance, saying to the people that they should believe on Him who would come after him, that is, on Christ Jesus.” 5 When they heard this, they were baptized in the name of the Lord Jesus. 6 And when Paul had laid hands on them, the Holy Spirit came upon them, and they spoke with tongues and prophesied. 7 Now the men were about twelve in all.