The trumpet and trombone you've listed are "pro" models, while the horn and euphonium are "intermediate"
If you're going to go "pro" on any of these, I would do it on the horn. We have Holton 279 and are very happy.
The rest would be fine with "intermediate" models like the Yamaha 4335 trumpet and the Yamaha 448 or Bach TB200 trombone, especially if budget is an issue.
On the tuba, we are very happy with the St. Pete's for a much lower price than the King.
I would advise that you DO spring for silver finish when you can get it. They tend to hold up better cosmetically than lacquer in a school setting.
All this is just my opinion. Good luck and I hope you get what you need.