Baby monitor advice from experienced moms

I currently have a decent video monitor (infant optics I think) for our 2 year old and it has the capability to add a second camera, and I believe it will flip back and forth between the rooms every few seconds or so. My other option is to buy a new separate unit, so I would have 2 monitors to take downstairs with me (but I don’t think I would need to carry them around much other than that), but then I could see/hear both kids all the time. I feel like this would be the biggest issue when baby goes into the room right next to his sister around 2 months old, I will want to go quickly when he cries so he doesn’t wake her up. Any advice or experience?