How would you handle having three forms in one page but only allowing the user to use one for input and therefore making the others inactive/disabled, in the most user friendly way.
Say for example having the user choose of one of the following forms:
Try a set of tabs. Only reveal the relevant form when the corresponding tab is active.
https://getbootstrap.com/docs/4.0/components/navs/#tabs
Give each form it's own submit button, enforces only one option can be submitted.