My wife spotted a one inch tear on the sail, about six inches from the foot. How do I mend it? What type of thread?
First a disclaimer: I'm not a sailmaker, nor do I play one on TV. All I can do is tell you what I'd attempt for a repair.
Which direction is the tear? If it is parallel to the foot, tension on the sail should be aligned and therefore not have a tendency to widen the tear. You may be fine with some sail repair tape.
If the tear is across (vertical) there would be some tension on it, and you'd reinforce the patch by stitching the tape. You'd want to use some polyester thread, to match the material your sail is made from. If you can't source good thread, you can unlay a length of polyester rope and pick apart one of the strands in it until you have something that is down to the thickness of thread (one or two doze fibers). That'll work in a pinch.
Sailmakers use something they call a "palm" that has a thimble built in that is convenient in pushing the needle through. They also have needles designed to push through sail cloth. For a small repair you can probably make do with a simple oversized needle and figure out your own way to push it through.
The deeper question is whether this tear is an indication that your sails are reaching the end of their life span. I would still do the repair, not least because it's good practice, but be aware that sails are consumables.
Finally, while you are at it, esp, if your sails are older, check the stitching everywhere, and if any is wearing out, redo it.