If you can ride the bikes in the conditions you'll normally ride them in, then do that. Some bike shops will let you and some bike shops won't. Mine did let me and the size bike I liked from just the parking lot ride was not the bike I liked after riding each for 10 miles.
Numbness in your hands and wrist was likely not so much about the size of your father's bike but more about how you hold your hands. Wrists need to be straight. You don't want the palm of your hand supporting your weight.
You might want to look at some of the cruiser style bikes from Trek if you are only going to ride for 20 minutes or so. They'll have a nice cushy saddle and a geometry for relaxed upright seating. And they tend to be very inexpensive too. But many bike shops might not stock them.
Welcome to BF. If you have a pic you want us to see before you get your 10 posts, just upload it to the
Gallery here on BF and tell us it's there. Or learn how to obfuscate the URL where the pic is hosted.