Maybe we are talking about different "Jesuses" here. I think it is necessary to distinguish between a possible royal Herodian prince (whose name wasn´t even Jesus but who may have acted out a "Jesus role" in his life) on one hand, and on the other the Jesus Christ of the Christian Church, introduced to the world as the only Son of God!
I can no way view them as one and the same, although the inventing of the latter may to a certain degree have been patterned on the life of the former, and although perhaps the former in his life had to play the part of a long-awaited Messiah figure.
First of all, the two of them were separated by two or three centuries. The Church and its Jesus Christ were in reality not fully established until after the A.D. 325 Council of Nicea, when the Roman Emperor Constantine gathered a large number of religious leaders in order to erect a unified and common religion that would appeal to the populace.
By the way, the Church of the Nativity in Bethlehem - one of the oldest churches in the world - was in fact not built until A.D. 330 by the Roman Emperor Constantine.
And secondly, there were different reasons why these "two Jesuses" were invented - the former one in order to legitimate Herodian rule in Judea, the latter one in order to give unto the Church its enormous and not-to-be-questioned power and authority.
The Herodian "Jesus" may have been born with the Sun in any fairly suitable zodiac sign, like Leo, Virgo, Aries, Pisces, and maybe even Cancer or Gemini, as you suggest, in order to legitimate the Herodian rule. However, the Christ of the Church - as separate from the Herodian prince - had (for astrological reasons) to be born at the winter solstice, the very Birthday of the Sun itself. There was simply no choice. Nothing less would do.
You are right - at least in part - about the Joseph association with Capricorn, although he has also been associated with the constellation Bootes close to Virgo, among other things. I think you are right also about there being competing biblical models of astrology. At least the whole subject seems deeply shrouded in a cloud of confusion.
© Charles N. Pope, US Library of Congress. All rights reserved.