What is the difference between IPA and Ethanol in terms of solubility? I have read an article online that says that ethanol could be used in a solvent extraction of two solids, but it also says that isopropyl alcohol could also be used, but must be used in higher concentrations. Why?

From some preliminary internet searches, I have discovered that:

"Isopropyl alcohol is a slightly bigger molecule than ethanol (Methanol is $\ce{CH4O}$, Ethanol is $\ce{C2H6O}$ and Isopropyl alcohol is $\ce{C3H8O}$) and is often cheaper to make. It is not as poisonous as methanol (an ounce of methanol can kill you and a third of an ounce causes blindness). So it is useful as a solvent in the same way acetone is useful as a solvent."

So would this suggest that if one were to use IPA as a solvent, one could use the same amount of IPA as they would Acetone?

One final question. It would be best to use 99% pure solvents (mostly free of water), however for an ethanol replacement, I have seen a product used for ethanol fireplaces where the MSDS mentions 95% ethanol and 5% 2-propanol. Would this be an acceptable substitute for 99% ethanol? Thanks a lot.
[...] ethanol could be used in a solvent extraction of two solids, but it also says that isopropyl alcohol could also be used, but must be used in higher concentrations. Why? [...]


They hopefully didn't write about the "concentration of isopropanol" but mentioned that a larger amount of the solvent has to be used.

It is not uncommon that organic compounds with polar substituents are less soluble in higher alkanols.

Vanillin is a typical example, the solubilities are in the range of 4.15 mol/L in methanol, 2.5 mol/L in ethanol and 1.8 mol/L in 1-propanol. (Data are taken from a freely accessible collection of experiments performed by students: OpenNotebook Science Challenge). I couldn't find any data for 2-propanol. 


  So would this suggest that if one were to use IPA as a solvent, one could use the same amount of IPA as they would Acetone?


No, not really. A ketone and a secondary alkanol, although looking similar on first sight, may have behave completely different as solvents. Polystyrene (foam), as an example is pretty much insoluble in isopropanol but highly soluble in acetone!