Hi Miley! Those sites are interesting. I have not yet knit my dog a sweater, but I have a couple pattern books for them! That first site says if you can knit a scarf, you can knit a dog sweater, but that does not count that you have to know how to decrease. However, that is not hard! There are good videos on this site of various decrease sts.
You can do anything you want but you can't do everything!
OTN: Berroco baby sweater in a twisty, splitty Berroco cotton yarn
UFO (one of several): Brown garter st swing sweater on hold unless we get another cold snap!xsigpic10708_3.gif.pagespeed.ic.Ims82L_-Zf.webp