Quoting May ♥:" Sorry if this sounds dumb. But how many blankets will 1 yard of fabric make? If I was just using said fabric for 1 side?"
1 yard is 3 feet. So if you're making an adult blanket, you want two yards or 6 feet so that it covers the average adult. 3 feet is fine for a child's blanket. So for your sister, you'll want 2 yards each of both fabrics. Then for cousin, another 2 yards each of both fabrics. And so on and so forth.