I ask such questions of my clients as a way to understand them, their situation and needs as fully as possible. No one is an island...we are a social species who are affected, for better or worse, by those in our social group, especially our families.
What I have seen is that parental/family input about homebirth can be an important factor in the success (or not) of a homebirth. Our parents tend to have such a strong influence over our emotions--and our emotions have so much to do with how we live, choices we make, risks we take. Not that someone whose parents disapprove of hb will be a 'poor candidate', or will necessarily wind up in the hospital, but if I know that a woman/couple does not have full family support for homebirth, that helps me know something about what we are up against (challenges to the birth) and how I might best give support to the woman/couple. For instance, in the absense of familial support, I will urge couples to hook up with online support, or hb supportive groups in real life in their region....because in a nation, and in an era, where hb is not 'usual and normal', people generally need *some* kind of social support to help them stay focussed on the positive, and remain confident in their choices...a place to vent about family pressures...stuff like that.
I've seen parents/family help tremendously with a successful homebirth--and I've seen them exert a lot of pressure to see to it that their grandkids are born in the hospital. Depending on the particular personalities of the parents involved, that pressure might be overt, or it might be covert...but it is there, and generally pretty powerful.