Is 1" clearance, insulation shield, etc. required for the larger pipe?

P4061176 (Small).JPG

I have a several questions.
The lowest lateral going into the stack. Is it for hot water?
The other the furnace?
Is this allowed on the same stack if it is hot Water.?

Lowest lateral line has 3 45% elbows.
The amount of degrees or turns in a gas or propane furnace or hot water exhaust?