When sweeping, there is two notes on the same fret, but on the next string, like say, 5th string 15th fret, and 6th string 15th fret. I have a really hard time rolling my pinky(I can do it with the other fingers) can I have trouble some trouble using my third finger as well, as my pinky is kinda in the way and the frets are small. How would you guys do this?

Practice rolling with your pinky. Build up pinky strength. It's the only way.

Even if you could more easily use the ring finger instead, it would be a problem later on with different/more complex sweep shapes.
Quote by HorizonShadow
Just eat the headstock.

That'll make you look mad.