You are on the right track with your thinking. We have discussed the subject of the firstborn and eldest son quite a bit here on the forum. I think the search utility is now working properly again, so you could check out some of the threads. I also go into this subject in Chapter 28 of the on-line book. See the section "All the Firstborn are Mine".
A royal princess would have been restricted to qualified royal males when selecting a partner for her premarital rite of passage. A royal firstborn was rarely sacrificed literally, but almost always sacrificed figuratively when it came to kingly succession.
There may have been some truth to the rumor that Jesus was fathered by a Roman. Technically all Herodians were Roman citizens and many Herodian princes were raised and educated in Rome. I suppose they might have also been allowed to participate in Roman military endeavors.
The name "ben Pandira" was discussed by Ahmed Osman in his book "House of the Messiah". He concluded that Pandira was a corruption of the Egyptian Pa-ntr-Ra, the god Ra. In the Hellenistic sense, all princes within the family of Herod were "sons of Ra". This is especially clear when it is recognized that Herod played the role of Solomon and that in Egypt Solomon had been worshipped as Ra. Pandira also bears a crude semblance to Antipater.
[I would be interested to know if there are any good Herodian genealogies on the web. Or just good summaries of the Herodian family and their partnership with Rome. Can somebody look into this and give us the results?]
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