Lightroom is designed as a single-user, single-computer system.
Lightroom Mobile will allow you to sync one computer with multiple devices (phones, tablets), but not with other computers.
The easiest way to work with your photos on multiple computers is to put the images and the LR catalog on an external drive and move the drive from computer to computer as needed.
If all your images are stored on the iMac's internal drive or an external drive that is constantly connected you can point LR on the Mac notebook to those images across your home network. But then they would only be available for editing when you are connected to your home LAN or if you built smart previews of them on the MBP.