According to Universal's website:
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So as your son is under 21 he cannot check-in, book or stay inside the second room unless there is a person who is at least 21 who has checked-in, booked and is also staying inside the room with him.
A possible solution is to split up you and your husband. Your husband stay in one room and you stay in another and you split up the family. Connecting rooms is something you could ask about though I don't know if you have to call them in order to request that honestly rather than doing that online.
There are a few options out there for suites though they wouldn't come with Express Pass included.
Have you looked into 2-bedroom suites at Surfside Inn & Suites? That resort opens up July 2019. In May 2020 the sister resort Dockside Inn & Suites is supposed to open up. The 2-bedroom suites do sleep 6. They are considered Value hotels but it still may be worth a shot to have everyone in the same room (take a look at the room layout too to see if it would work).
Cabana Bay, considered a Prime Value, has a Family Suite that sleeps 6 though it's not a 2-bedroom one there is a sliding room partition that can be used to create some privacy with the sleeping areas. Cabana Bay also has a Volcano Bay view 2-bedroom suite that sleeps up to 8 actually.
If the pricepoint was good for you you could add on Express Pass. Now that would be slightly different because when you book the resorts that come with Express you get it for length of stay whereas adding Express Pass when you are not staying at the resorts that come with Express Pass is a day by day process thus cost-wise it may not be as advantageous.
Just for informational purposes consider also looking into if 2-bedroom Hospitality Parlor Suites which sleep up to 10 at Royal Pacific, the 2-bedroom Hospitality Suites which sleep up to 9 at Hard Rock, a 1-bedroom Portofino Parlor Suites, the option with queen beds which sleep up to 7, or the 2-bedroom Portofino Parlor Suites which sleeps up to 10 which would come with Express Pass. These options greatly depend on your overall budget (including the overall cost for 2 rooms at these resorts) and availability for when you are wanting to go.