Yes, splitting the reservation will increase chances of someone getting upgraded. As long as you’re together, you will be passed over for people lower on the waitlist if PZ<5 opens. For example, if one upgrade seat is released, the first reservation on waitlist looking for 1 upgrade gets it. Not you or anyone on your reservation, who are looking for 5.

That being said, there’s no way 5 of you will be upgraded considering UA’s reduced F capacity to OGG. "If at least 2 don't get upgraded, I'll be in deep trouble with the Mrs..." - you might start thinking now how to diffuse the situation