You say 'The ash was struck by lightning about 15 years ago and regrew.' by that, based on how long ago it was, I take it that's an Arizona Ash, not the Texas Ash you planted. There's very little you'll be able to do for that one. It's never going to be very healthy. Same for the Silver Maple. IT grows fast, looks decently pretty for a number of years, then gets sick and begins falling apart, quite literally. I Bet your Texas Ash and Burr Oak are doing much better by comparison.
I'd look into cutting down the silver maple before it falls on something you're fond of. House, Car, etc. A Shatung Maple would be a great replacement.
That mulberry is likely going to be a problem. They are poor trees. The Sycamore is pretty, but can often have health issues here. If you're using the organic program it'll do better.
So, I'd write off the Arizona Ashes and the Silver Maple. Probably be a good Idea to knock out that Mulberry when you get that Silver Maple. Texas Ash and Burr Oak, good choices.
Shepherd of the Trees
It is not our part to master all the tides of the world, but to do what is in us for the succor of those years wherein we are set, uprooting the evil in the fields we know so that those who live after may have clean earth to till.