This is a good idea. It would be helpful to know when in the order of the family the person in the current profile was born.
However, I feel the marker O you suggest, and the presence of a comma before it but the absence of one after it, are not very attractive aesthetically.
An alternative in your first case 1) would be to change "Brother of" or "Sister of" to "Siblings:", then include "self," in the list at the appropriate point. An alternative to "self," could be the profile name without a link but bolded or italicised.