What needs to be done to save/return the trees to good health?

Since it's quite advanced in all the affected trees, there's little to be done at this point. This condition has persisted for at least a decade in these particular trees.

Does the nearest resident, at 3410 Kensington, need to request that the trees be removed and replaced?
Can I please ask who you are, CME? Or at least with which city department?

I am not with the city; I am an Advanced Master Gardener and garden educator with a particular focus on woody and native plants who has lived in East English Village 25 years. I researched this issue for a number of clients; you can as well. It's called "Black Knot Fungus".

https://en.wikipedia.org/wiki/Dibotryon_morbosum

Thank you for submitting your concern to the City of Detroit. This message is to acknowledge receipt of the issue you reported.

Thank you for using Improve Detroit. The City has implemented a new tree program for privately owned trees. If you are reporting a tree on your own private property, please use this form: https://app.smartsheet.com/b/form/7be4ea18b30046c2ba500e7e54ad6ea2. If you are reporting a public tree, we kindly ask that you submit a new request so that it may be investigated and addressed. We apologize for any inconvenience and appreciate your patience as we work diligently to resolve the outstanding concerns of Detroit residents.