Yes, you can share games with another switch owner by adding your account to his switch.
He will only be able to play the games using your account and cannot play the same game that you are currently playing at the same time.
Can you share downloaded switch games?
You can now share your digital Nintendo Switch games with other consoles. But only play on one at a time. You can now download and play your digital Nintendo Switch games on another Switch console with minimal fuss, thanks to a new system update. Playing on a secondary Switch will also require you stay online.
How does switch family membership work?
Family Memberships give up to eight Nintendo Account holders access to the Nintendo Switch Online service for a 12-month period. If you have more than one person to share the plan with, you can save on the total cost of the annual membership per person. The more people in your family group, the more you’ll save.
Can you play the same game on two switches?
To do it, one system needs to be signed into the account used to purchase the digital game. This will make the second console the account’s primary system. You can then log out of that account on the second Switch, and create a new profile. You can now play the same game on both systems at the same time.