A few ideas of what to wear. More can be found by searching what to wear images on Google.
It is best to avoid graphics and words on your clothes, especially in group photos. Also, wearing identical shirts/clothes is never a great idea. All white in a family photo washes out faces.
Some tips to wearing what you already have in your closets:
1. Pick one person's article of clothing that you love a build on that. Maybe pick a flowered or patterned dress for your little girl and draw colors out of that.
2. Coordinate, don't try to match. Many colors work well together, but don't necessarily match. Try pairing two bright colors and tie them together with a colorful necklace, scarf or headband.
3. Many patterns often make the photo look busy. Try one stripe, and one different pattern. Then go with solids to bring it all together.
4. Lay everything out on the bed. Mix and match shirts and accessories until you have a combination that you like. Make sure everyone's clothes fit before picture day.