Your best chance at getting the money back in an honest way (without lying about having Covid symptoms) would be to change the reservation to a nonconcierge cruise that is unlikely to sail in its current form (like an October 2021 7 or 8-night cruise, for example). Or switch to an upcoming Wonder cruise, since their guests haven't been given the "here are our new procedures & you can cancel if you don't like them" message, yet. Yes, you can change a concierge cruise to a non-concierge cruise. Switching to nonconcierge won't make your concierge deposit refundable, but it will keep the price of the 7-8 night cruise on a par with what you paid for your short Dream concierge cruise. When the new cruise is either changed to a shorter cruise or cancelled, DCL will then offer everyone, including concierge, a full refund. Switching to an upcoming cruise & getting the "here are the new procedures love 'em or cancel" email was how I got my February '22 concierge deposit back, myself.
There is no real risk in that approach, because Disney is currently letting people push their cruises further back even very close to cruise date. So even if the new cruise isn't changed or cancelled by DCL so no refund is offered, you can still push it further back to a later cruise date. The trick is to choose the earliest cruise you can (most likely to be disrupted by Covid) that is also a longer cruise. You also want to make the switch asap, because the cruise change or cancellation could happen at any time.
OP, you should also reevaluate your trust in the people who told you "concierge was the only way to go". I've sailed 6 non-concierge DCL cruises & can tell you that's baloney. They must have never sailed DCL non-concierge, to have said that. And did they mention the big risk of booking concierge, that you typically can never get the deposit back? Also, it would have been wise for you to sail DCL once yourself before booking an expensive extended family vacation on DCL. Live and learn. Hope our advice helps and you end up getting all of your money back.