It looks like these women tried to marry gravely ill "children" (i.e. guys who were old enough to leave orphanages and lived in their own state provided flats) and then tried to get a propiska there. Moscow "propiska" is a valuable thing. If it were possible a woman would have had the flat for herself after her ill husband's death (I messed up the tenses here, but I think you got an idea).
Basically it's an arranged marriage aimed to get "moscow green card" or to rob a former orphan of his flat in some other way.

Probably that's why a rule mentioned above was implemented (that an orphan can't register anyone in his flat for 5 years, except of his or her own child).