What you say makes perfect sense.In this case the Bible is actualy in agreement with Flavious Josephus(historian).I will proof using the Bible and logic,that Paul of the Bible is the same Saulus described by Josephus in Antiquities of the Jews Book 20,chapter 9,par.2 1)Paul was originally known as Saul(Acts 9:17) 2)Paul/Saul was from the tribe of Benjamin(Romans 11:1) 3)The name Saul is asociated with the tribe of Benjamin.Saul son of Kish was of the tribe of Benjamin and first king of Israel(1 Sam.9:21) 4)Paul/Saul was born a Roman citizen(Acts. 22:27,28).This explains the use of the name Saulus(the Roman form of Saul) 5)That he is related to the Herodian family(Romans 16:11).The Saulus in Josephus's writings is related to Agrippa(grandson of Herod the Great) 6)Why the name Paul? The Herodian name Phasael(brother of Herod) was shortened to form Paul,not uncommon in genealogy.The Roman form again would be Paulus.Both names Saulus and Paulus were used for Paul. 7)Costobarus was with Saulus and both regarded as royalty and related to Agrippa according to Josephus.Knowing al these facts Paul can be accurately placed in this family tree.See Wikipedia for chart"Costabar brother of Saul"