First, why downgrade instead of cancelling? Unless you've had the cards for a long time (which it seems you haven't, since you said you applied for the in last year), there's no big benefit to downgrading. With that many cards at Chase, if you donwgrade, you likely won't be able to apply for too many more Chase cards in the future, because they'll say "you have too many of our cards already". If you cancel, you leave yourself more possiblities in the future.

The one case where you might want to downgrade is if otherwise you'd be get rid of every card you have with a given bank. Then you might want to downgrade one card just so you have a contnuous history with that bank going forward, and cancel any other cards with the same bank that you don't need.

Second, if you keep the Chase Freedom you won't lose your UR points, but if you don't keep one of the annual fee cards, you will lose the ability to transfer (until at some point in the future you once get an annual fee card).

You can never get another SPG bonus on a personal card again, but you may be able to get another SPG bonus on a business card after a couple years. So if you are going to cancel any of the SPG cards, I'd say cancel the business card first, and keep the personal one unless you don't want to keep any SPG cards.

The United Exploer card's benefits will go away if you cancel (or downgrade) the card. But if your wife is the only who has it, then I think the benefits of boarding and bag may only apply if your wife books the flights and has the first name on the reservation. Except: The "lounge access" is simply two lounge passes a year, and I think those lounge passes (since they are not tied to the card once you have them) are still good even if you cancel the card (as long as their expiration date hasn't passed).

But you have the Amex Platinum, and its airline reimbursement won't work if your wife's United Explorer card is used to book! (That's the problem with several of the Amex Platinum benefits, they require that use that card to purchase travel, so you cannot at the same time use another card which gives you more "immediate" benefits on that travel.)