No, a spefic unit can be bound to only one account. For your case you can login the same Kasa account on both you and your wife's smartphone to share the same device

1. Make sure you have entered the correct password. Forget home wifi on phone and reconnect to check. 2. Change your router's wifi settings, such as changing wifi security or channel. 3. If still no...

All the new ones are with the problem? Have you made any changes on the router? I suggest to reset one of the old one to see if it can reconfigure successfully.

No way. Just mail support and suggest them.

You can do a test : 1. Creat a scene such as "Good morning" on kasa; 2. Delete kasa skill and then re-add kasa skill on google app. 3. you will see scene"good morning', say"activate good morning",...

http://static.tp-link.com/2017/201712/20171201/1910012261_HS100HS110_UG.pdf Flashing amber should be resetting, are you doing this?