Regardless of how much tread is left in the middle of the tire, you've worn off the sipes on the shoulder. So you have far less pumping ability and much greater chance of hydroplaning. Get new tires for safety

I would not get new tire, unless you are in an area that has lots of snow and ice. It does look like some wear is seen on the edge, could be an alignment issue or if the other is the same it could be under inflated.

Hard to tell. Make sure they are filled to the proper pressure and then give them the penny test.

Stick a peeny in the groove with Linciln's head pointing into the groove. If you can see the top of lincoln's head it's time to get new tires.

from the picture the tire looks fine how about the other tires and why are you asking?