I'm sorry to say that, as far as I can ascertain, the Rennie family ended with no direct descendants.
Isabella died in 1989, Eleanor in 1996, both unmarried and living at the same Glasgow address. Evelyn, who did marry and moved to Perthshire, pre-deceased her husband in 1975, and he died in 1988. The informant on his death certificate was a friend, not a relative.
I checked for offspring and could find none.
Thus endeth the story.................