It looks to me like your first step on GEDmatch would be to contact the first person on your match list there after your sister (it looks like she doesn't match your sister). At 130.2cM, they should be something like a 3rd cousin (3C).
The funny thing about THAT match is that her father is on your list, too, but only matches 40.5cM. Then her sister is yet further own the list, at 33.4cM. (Actually, with the two sisters being at 33.4cM and 130.2cM, they almost HAVE to be 3C to you.) All I can think is that you are more closely related to the sisters' mother than to their father, but that you're related to both parents.
Beyond that, though, something as Earth-shattering as this calls for throwing a few more bucks at it, and testing on AncestryDNA (with a subscription, too, at least for a while, so you can see the pedigrees of other people who have attached them to their tests. It's all about the matches for you, and they have - by far - the most people to match against.