Nice! You don't see enough "adorable" pieces like this of Rarity's family. I love how their Dad is rubbing Sweetie's head, and how Rarity's club is bent, (apparently she hasn't been playing well) but she still looks a li'l happy for Sweetie regardless. Even though we can't see much of the background, and the miniture golf course here, the design of the background looks very true to the show.
Y'know, Rarity & Sweetie's mother is one of the few ponies who wears pants. (Wonder why you rarely see ones who do wear them.)
And, what a coincidence, I'm actually writing a one-shot on the CMC about them playing mini-golf! I've been beating my head over it for the past month with very little progress, but this image has inspired me to get it finished. I would like to know if I could use part of this image for my story. Let me know if that's okay!
I just use a tablet and the toggle that allows you to draw smooth lines. I don't think there's a path tool in SAI, and I don't have a high enough photoshop version that has a pen/path tool. I don't really know all the ins and outs of SAI either, but if you play with it enough you can use it to suit your needs.