1) a. No.
b. This for me is murky. I'm assuming grown also means independent (out of the house, have jobs etc...) so I would give a tentative yes. FWIW, Hellen Mirren is in this situation.
c. No. If they actually were step parents, they accepted the reality of being parents, however begrudgingly.
2) a. Foster parents are still parents.
b. See "2 a."
c. They're empty nesters (or you could call them that), but they were still parents so no.
3) a. Yes.
b. IMO the bond is different (though tenuous I realize, so they can be.
c. Maybe. Again it's murky because with older siblings taking on a parental role it's not quite parents.
d. see answer "c."
4) a. This is hard, but depending o the circumstance maybe yes or maybe not. In a way you could say incomplete. More specifically do they already have children? Do they want kids in the future? What about a person who gives birth at 15 (for example), give the child up for adoption but later decides never to have kids. I would say yes. At that age, many people are still living with parents, so there is an external influence. I realize the answer is messy.
b. See answer "a." Given that it;'s women who give birth they have much more say in the subject. So incomplete or need further information.
c. This is murky. One part of me says you do the crime, you do the time. It's the whole be responsbile for your actions (aka sex can lead to pregnancy) but they might not actually want kids.
d. see above.
5) a. In my opinion, no. Infancy means they went through with the pregnancy/adoption and presumably bonded with it.
b. Usually no, but I realize the person may have wanted to give up the child for adoption.
c. Murky, so you need future information or background information. Do they have kids? If so, the answer is obviously not. But given that the question is intended to carry to term persumably they wanted to keep it so most likely not.
d. Murky. Need more information.
e. I answered this in some of my above answers, but maybe. Religion/culture is a huge influence (whether it should be or not), so the person may or may not be.
f. See 4. c.
6) They can be. Sometimes host families have kids and it's a trade (of sorts). eg. their child lives with the host family and that child lives with you. But it may not be the case.