U3818DW, setting up PBP with two laptops

Hi, 

I can't get this monitor to display correctly inputs from two laptops (using the full screen in native resolution) and I don't know if the problem is just settings/cable connections or that the laptops can't support the native resolution. The laptops are:

HP EliteBook 835 G7 (8RN40AV), with AMD Radeon RX Vega 7 integrated graphics, 512 VRAM and these ports: 2 USB-C (1 is Alt Mode, 3.1 Gen 2, 2 are Thunderbolt 3 compatible), HDMI 2.0., 1 USB 3.0

Lenovo Yoga X1 (20JD-CTO1WW), with Intel HD 620 integrated graphics, 128 VRAM and these ports: 2 USB-C (1 is Alt Mode, 3.1 Gen 2, 2 are Thunderbolt 3 compatible), HDMI (not sure which version), 2 USB 3.0

What's the best way to connect this laptops in PBP mode?

Thanks!