How many unrelated people can live in a single-family home in Orem? Are there same rules in Provo?

It's 4 in Salt lake. Call the city of each town and ask - the rules vary city to city

I was able to find out myself: 3 unrelated people or 1 single family can live in a single-family home in Orem, Utah.

It's 3, related or unrelated in Provo.  However, there are many properties that are closer to BYU campus that have grandfathered in a "batching singles" designation that can be between 4 and 6 per unit.

Nice--good to know!

As many as they can cram in the house . 

Quick note. Look up parking as well. There are often issues on units that allow 3 singles but only two parking spaces. The zoning official can tell you but also CCRS may play a role as well.