Interested in the research
There is becoming more and more research on Systemic constellations in English. There is a lot of research in German and other languages.
Here are some I have found in English
The Handbook of Systemic Family Therapy, Set
Karen S. Wampler, Richard B. Miller, Ryan B. Seedall, Lenore M. McWey, Adrian J. Blow, Mudita Rastogi, and Reenee Singh
There are many dissertations on Systemic constellations and Family Constellations if you can access academic papers.