I've been trying to connect three monitors to Mac and PC for ages and it finally works , provided a solution that worked. Connect the supplied cable from the computer to the KVM. Connect the other HDMI cables that came with the kit to the monitors.
TESmart 1080P 60Hz USB VGA KVM Extender Over Cat5e Cat6 Ethernet Cable - Long Range 984ft/300m (Sender+Receiver)
10 Review
4 Port USB 3.0 Switch Selector - Pubioh KVM Switch for Mouse, Keyboard, Printer, Scanner - 2 in 4 Out Sharing Box with Switch Button and 2 USB 3.0 A to A Cables
11 Review
CKL Quad Monitor HDMI KVM Switch 4 Port 4K@30Hz with Cables - Extended and Mirrored Display Support for Windows, Linux, and Mac
11 Review
Enhance Productivity with CKL HDMI KVM 2 Port 4K 30Hz Dual Monitor Extended Display (CKL-922HUA)
10 Review