Will Marvin epub reader work on MacOS Sierra?

You cannot run an iOS app on any computer. You need a separate version for the Mac or PC. If there isn't one, then it will not work. A good substitute might be calibre 2.80.0.

How To Safely Use Macupdate To Download Ad-Free Software

This site has both free and paid membership accounts. If you have neither then some software will be distributed as an installer wrapper that includes adware/malware you may not want. Such a download may appear on your computer like this: Firefox Installer.dmg. Delete the download and return to the main site where you will find a direct link to the developer's website. Use that link from which to download the software. Or a simpler way is to establish a free or paid membership to avoid problems getting adware with your download.

In addition to the fact the you cannot run iOS apps on a Mac - or vice versa, Marvin being an ebook reader is intended to read text based books and not comics/manga/graphic novels. They even have different file formats and file extensions. For 'comics' the two main file extensions are .cbr and .cbz some may also come as standard PDF files.

What you want is generically referred to as a comic reader. Some examples are as follows. (They are not all free.)

http://www.yacreader.com/

http://dancingtortoise.com/simplecomic/

http://comical.sourceforge.net/

http://www.bitcartel.com/comicbooklover/index.html

http://www.comicnerdapp.com/

…there are lots of others.

I suggest that you contact the App's developer: Appstafarian, to find out, if and when, they will be providing an macOS version of their applet.