How do I get the Wi-fi calling option on my iPhone 6

The ability to turn on wi-fi calling in Settings is dependent on your carrier settings. Go to Settings>General>About>Carrier and see if the settings on your phone and your husband's are the same. Do you have the same carrier file? If not, then see this support document for instructions on how to update carrier settings. The carrier's file is what determines what appears in Settings and what you can turn on and off in regards to cellular/mobile. If they are the same, then you will still need to have the carrier check, since they are the ones that provide the carrier file. The worse case scenario is that you will need to restore your iPhone to factory, and set it up as as a new phone to see if the carrier file correctly updates. Restore your iPhone, iPad, or iPod to factory settings - Apple Support