I do believe you have it hooked up correctly. Is your gang valve adjustable? I have to adjust mine because the pump will put most of the air in the location that is hooked up nearest the pump and will not let enough go to the furthest hookup. What I did was to restrict the flow to the first hose therefor more was sent to the second hose. Another thing could be that your air pump does not have enough power to send air through all your hose. You could also try shortening the hose so it does not have to push the air so far. I hope this helps.
Adding to what Megan said, sometimes those plastic air valves don't work very well. Try blowing through the air line to see if there is a clog in the valves or the ornaments/air stones. At least that will show you what part is not working.
I was having the issues when i hooked everything up with my Hawkeye 201 air pump from my 1 gallon tank.
I did a test of hooking up the air pump that had come with the mini-bow 2.5 (Which was to powerful for the tank and to loud... That's why I was useing the air pump from my gallon tank)
Both the air stone and the treasure chest w/diver worked then.
So I'm guessing i need a pump that is just a little more powerful.
Trick is getting more power and still being quiet.
Some air pumps just make noise, and some make noise when there is too much back pressure. Maybe this will work: Hook up the larger pump, and add one more valve to the system. The new valve will be a bleed valve to relieve some of the pressure if there is too much. You should also install a check valve (one way valve) to prevent a back syphon in the event of a power outage. Put the bleed valve between the pump and check valve. You can operate without a check valve if the pump outlet is higher than the aquarium water level.
Please don't get discouraged. Aquarium keeping can be confusing and difficult at first, but it gets easy and you'll be glad you stuck with it.
If the valve isn't adjustable...
I use the old fashioned... pinch the line in two... and hold it with a rubber band, then wiggle it so that it's open enough for enough air to go through to power the ornaments.