I enjoy using OBS as a visual mixer with 4 inputs: 3 cameras and 1 PowerPoint.
Currently, I’m using CAMLINK as the capture card, but it tends to overstretch my laptop’s USB hub, causing connection drops.
Does anyone know of a way to handle 4 video inputs on my laptop without needing an external switcher like ATEM or DeckLink?
…Thunderbolt (Hub) instead of USB…
What kind of cameras are you using? Some cameras have RTMP streaming capability built in and you could try to stream video feed via network with cost of some added latency and network setup.
Also try different port combinations to change distribution of cameras to different lanes of your laptop motherboard.
Thunderbolt? I’m using Microsoft Surface 3, it does not support it 
I’m using DSLR’s (Sony a6400) I’ve got a few of them.
based on the specs of everything mentioned your best bet is to pick up separate hardware mixer. there could possibly be some kind of standalone usb c based capture card that does at least 3 simultaneous hd inputs better than stacking el gatos, but it would most likely be just as or more expensive than just grabbing an atem