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SurveyJS
Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
The Shared Vision module will give you finer control over things like this.
Here's a curve ball, though - my preferred way to manage this issue is to use Token Lean - lets players hold down a key and move the mouse around to sliiiightly tweak their own field of vision. It's intended to use for peeking around corners, but it's generally good for letting you glimpse things that are just barely out of view. It won't help if players are on literally opposite ends of the area, but in that case, I'd be wondering, who on earth got so badly out of position? :)