You can embed your iframes easily using a Section field. Just add one to your formaloo, go to the Source from the View menu, and paste your iframe code into the Source editor box.
You can also change the width of your iframe by editing the width and height properties in the iframe code. A 100% width makes sure your iframe takes up the whole width of the container.
You can also embed different web pages (like your calendly page) in an iframe. Here's an iframe template code you can use for this purpose. Just replace your web page link inside it to work.