So, they don't just form very small micelles within the body of the, well, liquid of which there's more there?
I don't think they would. After all, olive oil and sunflower oils are themselves mixtures of several different fatty acids.
if their amounts are comparable, they will just separate according to gravity
Not if they form a solution, which I think they do. After all it's not like if you leave a bottle of vodka alone all the water will sink to the bottom and all the ethanol will float to the top.
Ethanol has that OH group. It's a polar molecule, and a small one. But take two pure long-chained fatty acids, mix well, and then what will happen? (I said "oils" to show I didn't mean a "hydrophobic in polar" solution, which I hadn't thought the question implied.)
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