I tried this custom question theme for sliders with control buttons by tpartner:
github.com/tpartner/LimeSurvey-Slider-Controls-3x
These control buttons are very user friendly. Would it be possible to implement such control buttons in a normal "multiple numeric input" question without slider layout? I made a retouched picture to show this idea:
In my case, ideally, the number increases/decreases by 2 if someone clicks 1 time on the control buttons.
So that users do not have to use the keyboard, they can also use the control buttons to enter something in the "multiple numeric input" question.