Family friends are simply that, friends of your sims family.
That is an easy one! In the lower right you have a crystal and the needs(the left of the needs is the crystal) and below it you have few more icons. Click the relationship icon. And you will see pictures of your sims friends and family, lovers, best friends.... The one that has a red hearth below their picture. In that sims your sims is in love with!
You could make your family, your friends family, celebrities, the neighborhood family's or you could just muck around making weird family's do crazy stuff or kill them! It's up to you!
Infinite.
You make your sims best friends,
Yes, your Sims can get married and have children together.
No, you cant remove any of them. The only way to remove a sims from the family though it to kill them.
8 sims maximum
Start a Family
You can have sims get married but they can not have children
If your sims are already best friends, flirt with or kiss them. If not, get them best friends while flirting/kissing them
No, Sims can not have relationships with anyone they are related to.
yes, it is the sims bustin' out