I make napkins all the time. I first used a serger but didn't like the corners. I have two different rolled hem feet for my Viking and have stayed with this method. If the fabric is light in weight I use the narrower foot and if fabric more sturdy then I use the wider foot.
I also clip the corners off about a quarter inch or so to decrease corner bulk. I would practice on some scrap fabric that isn't as large to get your corner how you like them. Be patient and you will love the process.
Thanks for asking. Karen