One out of four speakers connect. The rest will not.

I think the reason you’re having so many issues is that you factory reset the speakers. That tends only to add confusion, and basically erases any information stored on the speakers that could help Sonos figure out what the real issue is.

There’s some information missing that might be helpful, though. Is this a mesh network of some type? it’s possible that some speakers are trying to connect to different subnets (but the same SSID) which would mean they can’t connect to your controller device.

Do you have the ability to wire one of your speakers directly to the router? That would be the best way to resolve many of the potential issues here. Or, failing a speaker, a BOOST wired directly would do the same function, creating a separate SonosNet signal that all your speakers could connect to.

Depending on some of the setup, it’s entirely possible that you may be better served by creating your own network, by using a travel router to connect to your landlord’s wifi, and then adding all your own devices to that network that you control, but that really depends on how the situation really is. I’m kind of throwing out all possibilities so that when we get the real knowledge, we can jump in any direction needed. 

I guess It’s quite possibly the case that the landlords new router uses ‘QOS’ or/and some kind of ‘Airtime Fairness’ and that those features, or some other router settings, are ‘perhaps’ causing you these setup problems.

Maybe start by asking the landlord to check and see if they can perhaps kindly check and disable those features (if applicable). If not, then consider maybe using your own travel router linked to the network instead and see if that resolves the issue.

Just spoked with him and asked if his system was working. He had no problems moving his Sonos units over to the new network. 

He might have his running on a SonosNet connection in that case - do you have the option to cable the one speaker that you have setup already to the LAN? If so, then perhaps just try that and see if a wired SonosNet link works for you.

I recently encountered a system that could not connect things. The controller asked me to reset this and that, and fuss with WiFi. Wiring units to the network was ineffective. All the while a network scanner showed all of the units were online. Another controller had no trouble with the system. Final resolution was to uninstall and reinstall the iPhone controller.