How are you and hubby handling the speed difference now? He must be slowing down, or you'd not be riding together! (for long)
Things that will help speed you up:
Tires, as mentioned. But only if they are supple, low rolling resistance tires like ReneHerse. (formerly Compass) I like the Stampede Pass 32's on a hybrid. They aren't cheap, but are likely the best rolling ties you can get without going to tubulars. And the ride is extremely nice. Cheap narrow tires will help very little, and give an awful ride.
Lower body position. Lower the handlebars by removing spacers and/or flipping the stem. Narrowing the bars will help improve aerodynamics too.
These changes are likely to only offer you 1-2 mph increase at best. For more, you need to strengthen the motor. Train more!
Another option is to hook hubby up with a trailer. Load with kid/dog/weights as necessary!
