You can sand them down and redo it lighter. Or you can try some kind of wash, but you won't get the look you were going for.

They'd have to sand them down and restain. The color looks okay to me so unless you were trying to match a certain wood color somewhere else in the home I'd just accept it as it is.

I agree that there is no easy way to lighten them short of a complete sanding. And the amount of effort to sand in complicated areas, like around those stair spindles would be huge. Even though it's not your desired result, trying to change it would take a whole lot of effort and money, and you still might not end up where you wanted. I'd learn to love them as is.

Did your flooring expert offer stain samples (on the sanded floors) for you to inspect/choose/sign-off on? If not, then a very big step was missed.

I'm sorry but lighter means REDO. Complete. Redo. If the stain sample was NOT provided, you can talk to the professional about splitting the costs.

If you were given a stain sample and you gave it the "OK", then the cost of the change will be carried by you - the homeowner.

I understand that your samples show a much lighter wood and that you were expecting the "same"....but not all stains can do this. Not all species of wood can carry this colour (this is gray/brown = SUPER HARD TO MAKE). And not all flooring professionals can achieve gray....in fact only a small handful will have taken the courses to LEARN how to make gray.

I wish you luck. Photos of the rest of the flooring around the stairs would help.

I have gotten myself into similar situation. Were you able to make changes without resending? Or accepted as it was done.

To go lighter you must sand all the finish off, basically starting over with one layer of your wood removed and one less refinish down the road because of it.