Wow--some very interesting partner possibilities for this gen! I have found cake to be a great equalizer when it comes to teen/YA age discrepancies---if the relationship is working out. In fact, since my TJ family all have the doubled life-span due to a genie wish, my heir grandparents spend a lot of time visiting their kids/grandkids and providing birthday cakes, to keep all the spare grandchildren approximately the right age. Though that has proven to be more difficult as no one likes to stay home in my last few towns. I've even resorted to inviting half the town to a birthday party and having multiple birthdays just to get kids ages in sync again. Or, in the case of partners, the same age again. Watchers must do what they must for their charges! lol I can't wait to see how it all plays out for your three teens!
FYI: If a sim has the Brave trait they will violently reject it when another sim uses 'offer to protect' and a Coward sim will get upset when 'ask to protect' is requested of them. I'm not sure if any other traits affect that but those are the two where I've seen that action rejected.