Hello,
put both PDFs into one file, the front side first and the back side second, for example with the Merge PDF tool: https://tools.pdf24.org/en/merge-pdf
Then print the merged PDF and choose double-sided (duplex) printing in the print dialog or in the settings of your printer. Page 1 ends up on the front and page 2 on the back of the sheet.
If the leaflet should be folded like a small booklet, the Booklet tool arranges the pages for that: https://tools.pdf24.org/en/create-pdf-booklet