Unfortunately, for mangas like these (smut) they like to list chapters as "volumes," not all but some do. Not the type of volumes that we typically understand, which are a compilation of 1-4+ chapters. As for the 48 chapters you see on Japan Renta or other sites it's because the chapters have been cut shorter for mobile use (android/iphone). For example instead of a whole single manga page they split up the page in sections/parts. This option is also cheaper for users that prefer to rent rather than buy. I've also noticed that Renta Japan has released another version with color manga pages for this series, which have been split into sections as well. I hope this answers your questions. I myself purchase all my manga from these sites so I had a chance to read the ending of this series.
This is series is one of my guilty pleasures. I've read other "beastman" smut stories and by far this one is the best. The art is cute and the character's are likable. The smut scenes are not cringey. Sadly, though this series is cut short at only 16 chapters. So no wedding or babies. I know I wanted to see it too. This story has so much potential, honestly. Oh well...by the way the English scans were taken from Renta manga-- a paid site. Please support the artist if you're a fan.