Dual monitor setup between MacBook Pro and MacBook Air

If these Macs are recent enough, one or both may support being set up as an AirPlay Recever for AirPlay to Mac.

Continuity features and requirements for Apple devices - Apple Support

This is not as good as a first-class hardware-supported connection to a monitor, and there may be lags, artifacts, and/or limitations on available resolutions.

A typical full speed display uses an unrelenting data stream, typically 15 G bits/sec or higher.

Your wireless network can provide around 1 G bits/secs, and typically less.

If you want a responsive, full speed connection, wireless is far too slow to be part of the answer, no matter what you are trying to connect.

By impersonating an external display, the Luna Display device accepts a full-speed display output, and converts it to a more manageable (and far slower) data stream that can be sent over a connection like your home network. Luna Display software on the remote device recreates an equivalent display image.

Luna Display technology can NOT achieve performance equivalent to full-motion Video, regardless of what their marketing materials may say.

Are you talking about sharing external monitors? Or about using one computer as a display for the other?

There's a dongle for that. Whether or not it delivers the performance you are looking for, I can't say.

https://astropad.com/product/lunadisplay/