When you honor someone by giving someone else their name, your love for them must be fierce enough to envelop their name also. As you think the bump in your husband's nose, which you initially considered awkward and wished away, the most beautiful feature any face could have, because it is his nose on his face. Because you are you, because it is it, that is love. The Thing In Itself. It-ness of it. Quiddity.
Donald is Donald, the thing in itself, beginning with its own quaint and dated syllable, tumbling over the hill of the n, rumpling into the nd at its base. It is everything it is, ancient, Scottish, both craggy and cushy at once. It is The Thing In Itself, its proclaims its donaldicity to the listening hills, birth certificates, gravestones, driver's licenses, report cards, signatures. It is nothing but itself.
If you go to honor someone using their name, it must be because your love for their name has overflowed from your love of the person. The person's quiddity. You must fiercely love the quiddity of Donald or to use it means nothing, and to use it in some horrible modern compromise-bastardization means absolutely nothing at all. Brydon takes everything which is Donaldic about Donald and washes it away. It is like Heidi Montag's plastic surgery. Worse, even. It's like on sims where you have randomized to come up with a cool face with a wonky nose and big lips and skinny eyebrows, and then click on the first default face and watch it spring and wobble back to a completely inoffensive, anonymous shape. And you call it the same Sim because it's wearing the same clothes as before. Brydon is nothing, it does not exist, it is like an empty chip bag. It is a name, a non-name, borne out of two compromises - three if you count the one to the stupid whims of modern fashion. It is like staying at home and doing nothing. It is like not using a middle name at all.
One must have courage. Brydon is not Donald. It is not Bryon. It is not honoring at all. It has made honoring a slave to the parents aesthetic preferences, which is not honoring at all. Have you ever had something published and, when you read it, found that it had been edited without your authorization to take out all of the interesting parts, all of your stylistic quirks, all of the quiddity of your work, but kept your name on it? That is Brydon.
If your fierce love of the person does not overcome your fierce attachment to aesthetics, that is a totally legit sentiment. But then, you should not honor at all. You know silly putty? I feel like if everything in the world were compromised it would all look like silly putty. Brydon is silly putty. Have I made it clear that I do not approve of Brydon.
I went through a similar thing myself. My granddad's name is Larry Stephen "Steve." Two names I did not like at all. I thought for a long time that Laurentius was honoring him. Ha ha ha. no! The Thing In Itself. So I grew to love Stephen, not as a compromise, but on its own terms, its quiddity, the ph, the st, the long e, everything it is. Similar thing with Ludwig for Beethoven. Etc.
...I do cut this concept a little leeway on different translations of the same name. To me Maria/Mary/Marie are the same name. So I could see using one of the more celtic forms of Donald, maybe. But Donald would be best.