Nice piece. As a healer/seer and astrologer, synastry is the relationship (angles) within oneself and with others.

In my most recent past life I died in the early 1940s as a Polish Jew, working with the resistance and had an untimely end. I was a double or triple Virgo (Sun, Moon and Rising Sign). In this life I have a Virgo Sun, Moon in Libra and Sag Rising. I didn’t find out about my last past life through astrology. I explored what “I saw” and correlated it with astrology after the fact.

One factor in confirming a past life connection with another person is a look at the lunar nodes placement or in the birth chart the north and south node. The south node is the past in this life and past lives and conversely the north node is about the direction forward.

A good book on Nodes: "Karmic Astrology: The Moon's Nodes and Reincarnation" by Martin Schulman".