I am assuming that I can contribute to the family limit for both 2019 and 2020 based on the information in this thread and this excerpt from the instructions for Form 8889 (https://www.irs.gov/pub/irs-pdf/i8889.pdf:(
"If you were covered by both a self-only HDHP and a family HDHP at the same time, you are treated as having family coverage during that period."
