I think my iMacs aren’t getting online within managed or standard users but the admin accounts are. We’ve had some network issues in the past.
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While it is possible to apply parental controls onto a managed user on a mac from an administrator account, generally the parental controls do not block the internet.  They only filter sites.  If a person is within a parental controlled user and is trying to access a site, they would be prompted that the site was blocked.  Not “just not loading”.  This leads me to believe strongly that there is another issue at play.  There is currently no possibility of a virus on two macs that would prevent access to the internet.  The closest thing to a virus a mac can get comes in the form of a browser plugin  that actually routes traffic in a different way so the user is presented with a different set of ads within that browser.  This plugin must be installed purposefully by the user and the admin password must be entered therefore it is not actually a virus, more so just a really bad plugin that people are tricked in to installing on their own machine.  By definition, a virus is something that installs on its own without the permission of the user.  This does not currently exist on macs.  Nevertheless, this was not the case on your office mac.  Nor is it the case with my own laptop, iPad and iPhone.  All which exhibited the exact same behavior when connected to the network before discovering the other device.  

I would suggest not mixing router or extender brands.  In other words, I have found it best to only use one manufacturer’s brand router within a network.  This is to say either all apple routers, all linksys routers, all netgear routers, all d link routers, all belkin routers, etc…  I have not had good experiences where there are more than one brand router working together to display the home network.  

Secondly, when troubleshooting network issues, I’ve always found it a good practice to abandon the network name when reseting the network.  For example, if your network was previously called Smith Network, the new network would be called Smith Net, New Smith, Family Net, etc…  But not Smith Network once again.  I have found that this can also cause issues.  Certain devices that return to the network later can become confused upon rejoining.  It all comes down to the one router’s ability to hand those numbers out we discussed called IP addresses.  If a device was given a number a yesterday under the smith network, then the smith network changes in some way, when the device returns it can be a little like talking to the identical twin.  One device expects the other of having knowledge of the prior conversation while the other device is offering a new number.  It’s always better in my opinion to just start fresh with a new network.