Husband's hair transplant

My husband has been experiencing hair loss since his twenties.

I even considered whether I should wear a wig at the wedding.

I'm okay, but it seems that my mother-in-law is very upset about her son's hair loss (baldness).

She is telling her husband to get a hair transplant as her lifelong wish.

Do I need to have a certain amount of hair on the back of my head to undergo a hair transplant?

But my husband has thin hair on the back of his head, so there's no hair to use from there.

Is it possible to transplant someone else's hair when performing a hair transplant?