My double leg takedowns happen more by luck then skill but they still have an advantage to the single leg takedown.
Getting both legs means i have more control over my opponents base and center of gravity.
Meaning i snatch their feet out from under them or easily lift and carry them out.
If you want to get a double leg then i would say start with getting a single and then work from there.
Or fake being afk and maybe you can clap on the legs.
I wasnt faking though.