@Cee_Cee 

Quick things to look at:

• Did you have an old router? If so
• Are you using the same SSID's? Change the SSID if  you are.
• Did you power everything down including the device after you connected the router?
• Have you tried Forgetting the Network on the devices?
• What is the Security Setting on the Router?
• How far away are the failing devices? Does it match for the devices?
• Have you tried different Channels for the SSID? You can check the channel congestion using a Lan Analyser, like Acryblic Home.
• Are you using Smart Connect?
• You can test with no Security. Turn on Guest SSID and see if the devices connect to it, would rule out mismatched securiy settings.