So just helped one of my friends with something like what your talking about, for their system 8 cameras a mix of Dahua and Amcrest and a different brand POE doorbell, Not going to mention brand because I don't want to endorse it.. But it is a Hikvision OEM. Anyway set them up on the 4216E-E1 NVR that has 16 POE ports and the Ai cameras used their own Ai and for the doorbell seeing it didn't do anything for its human detection as it wouldn't in your case. Let the Reolink do its thing in the app but as for the NVR like we did for his, using one of the channels if Ai from the NVR setup an Intrusion for the doorbell and he gets his alerts in the doorbell app and also gets the event recorded on the NVR.. Because your Reolink and their POE doorbell are not Dahua button push or any PIR that it might offer will not translate to the NVR..
So for your brothers house, I would get 4216E-E1 or if they don't think they would even grow to any amount of cameras over what they have look at the 4208E-E1 if they have that format or even the 52xxE-E1 format for an Ultra NVR that support Ai cameras with loads of horsepower.. They could get away with something if they wanted to go little lower in horsepower down to a 4108E-A2 This is what I would call a Lite NVR and would work great for your brothers 3 Ai cameras and Reolink Doorbell, Only down side is there would be no Ai for the Reolink and would have to use motion for events.. IF you want Ai for the doorbell then 42xxE-E1 or 52xxE-E1 is the best bet..
Edit, I keep saying E1 but it is EI (i) sorry for any confusion in the matter.
