Is it possible to insert three Grid Edit reports from three different tables into a Dashboard page? Should I use a iframe solution?

QuickBase does not need to support Web Components - only your browser needs to support it and eventually will. In fact, this <textarea> which I am typing my reply into is in fact composed of two <div>s in the hidden Shadow DOM. Check the web inspector screenshot I have attached if you don't believe me.

As used with QuickBase, Web Components will allow you to create custom tags which you can drop into your dashbaord text section and import blocks of functionality such as a report. In this style:

<qbreport dbid="foobarbaz" qid="6"></qbreport>