What happens to my old 2 GB plan after I join a family plan with my husband

See the following from Share an iCloud storage plan with your family - Apple Support

If a family member is already paying for their own iCloud storage plan, they can choose to switch to your plan or keep their own and still remain part of the family. When they switch to the shared family plan, they get a refund for the remainder of their personal plan. They can't keep their current plan and use the shared family plan at the same time.

Follow these steps to switch to the shared family plan on an iPhone, iPad, or iPod touch:

1. Go to Settings > [your name].
2. Tap Family Sharing, then tap iCloud Storage.
3. Tap Use Family Storage. 

Follow these steps to switch to the shared family plan on a Mac:

1. Choose Apple menu  > System Preferences, then click Family Sharing.  
2. Click iCloud Storage.
3. Click Use Family Storage. 

If you're using macOS Mojave or earlier:

1. Choose Apple menu  > System Preferences, then click iCloud.
2. Click Manage Family. 
3. Go to My Apps & Services. 
4. Click Use Family Storage.