For example, if two people fell in love and their respective families not allowing them to talk or interact at all
If the individuals are adults and the parents forcibly imprison them to prevent interaction, that is a crime in most jurisdictions. If they are children, this is generally allowed under the rubric of parental rights and responsibilities, although there may be local limits on what control a parent can exercise. It is also possible that one or both parents may abdicate their supervisory responsibilities in favor of e.g. grandpa's rulings, but grandpa has no legal right to overrule a parent (unless they are in fact the legal guardian of the child).
If we are not talking about forcibly preventing interaction, then anyone has the right to persuasively prevent social interaction. Such persuasion can take many forms, such as limiting the child's access to internet service provided by others. This still leaves the child free to buy their own devices and services to maintain contact with their s.o.
So the primary legal distinction is between using force against a legally competent adult, vs. using force against a child or incompetent adult or using persuasion.