YOU SAID:
Once upon a time lived a person who existed and then a frog ate them
INTO JAPANESE
昔々存在していた人が住んでいた後、カエルがそれらを食べました
BACK INTO ENGLISH
Frogs ate them after people who lived long ago lived
INTO JAPANESE
カエルはずっと前に住んでいた人々が住んでいた後それらを食べました
BACK INTO ENGLISH
The frog ate them after people who lived long ago lived
INTO JAPANESE
カエルはずっと前に住んでいた人々が住んだ後にそれらを食べました
BACK INTO ENGLISH
The frog ate them after people who lived long ago lived
That didn't even make that much sense in English.