Here's a question: What if something different and weird happened. Let's say the son instead held the intruders at gunpoint and took away their weapons. Then he ordered them to disrobe, bend over, and raped each of them. He then called the police and they came to arrest the burglars. Upon learning of the rapes they also arrest the rapist son.
Does the getaway driver get charged with three counts of rape?
First, there's no statutory framework (at leat that I am aware of) for that posit so no. It's also difficult -- for me at least -- to envision a fact set where the defender raping an intruder would be objectively reasonable (ie necessary, immediate and proportional.)
A more realistic scenario would be the intruder forces one victim to sexually assault another. In that case (with the understanding that this would be a fringe set of facts and outcomes could vary wildly according to statutory interpretation) the person actually performing the rape would have the benefit of the justification of compulsion (well-established), the intruders who are actively compelling the victim could be guilty of rape under the theory that they used the victim as the penetrating object (or whatever statutory element applied) and the accomplice could be seen to have aided, abetted the commission or criminally aided or abetted after the fact for assisting in evading capture, according to the level of participation and knowledge.