Red-green color blindness is an X-linked recessive genetic disease. That is, it is a disease that is caused by a particular allele of a gene on the X chromosome that only expresses when all copies of the gene are the disease allele. Since women have two copies of the X chromosome while men have only one, it's much more likely that men will have this particular form of color blindness. Women with one disease and one healthy allele do not suffer from color blindness but may pass it on to their children; they're called "carriers."
This diagram shows a family tree for a family that suffers from red-green color blindness. (Hopefully it's hypothetical, given the extreme level of incest and inbreeding!) Squares represent women and circles men. People with the disease are colored red, healthy people green, and carriers white. Some people's genetic status isn't filled in, and instead is indicated with a question mark. You can't make any assumptions about the disease status of anyone not shown on the tree, they might have any alleles.
The family tree as shown is unambiguous: There is only one possible genetic status for any person shown with a question mark.
The family tree encodes the fractional part of the minutes of latitude and longitude; your job is to figure out how. The posted coordinates are for parking, but have the correct whole part of the degrees and minutes (N47 31, W121 55). The cache is located near the Preston-Snoqualmie trail not very far from the trailhead near the Preston Ballfields Park (and the sun of Sam's Solar System). It should be an easy walk. As you're approaching the cache from the direction of the parking coordinates, it's an easier approach if you don't head directly for it, but rather walk a little past the coords and look for a side trail heading in the right direction.
The difficulty rating is entriely for the puzzle. The hide's an ammo can and shouldn't be particularly difficult to find, although that doesn't always seem to be the case.
There's a fairly steep hill near ground zero. There's no need at all to go over it, the cache is at the top.
Don't forget that the longitude degrees is 121, not 122 like most Seattle-area caches.