Hey Josef,

If I am not mistaken, I think your intention is to add several custom fields to choose your family members from user search during registration only for a particular group and also send a family member request to those users once you added them as family members.

If this is your intention, unfortunately our custom fields currently does not have this feature.

But, since it sounds like an interesting feature, you can definitely submit a feature request regarding this in our voice page -> http://stackideas.com/voices/easysocial, so everyone else could vote for it, the more people request this, the more we will consider it.

However, if this is not your intention, kindly enlightened me on what exactly you are looking to achieve with custom fields. Thanks.