Here are a couple of recent sibling shirt sets I have done. First for my niece and new nephew:
Big Sister and Little Mister designs are both from Embroitique. I added their names with 8CP's High 5
MCA's VINTAGE sibling set. I love the look and the quick stitchout of vintage applique letters, I'm so excited she released this version! I added their name with MCA's Angelina.