Here is the full list of all 45 The Sisters - there are Party of the Year achievements worth 1,000 gamerscore.
You have finished The Pixel Sisters on the console in the living room
Collect all the flowers in adventure mode
Collect all the coins in adventure mode
Collect all the mushrooms in adventure mode
Collect all the figurines in adventure mode
Pick up all the collectibles in adventure mode
Finish all the "Race" quests in adventure mode
Finish all the "Fishing" quests in adventure mode
Finish all the "Investigation" quests in adventure mode
Finish all the "Search Area" quests in adventure mode
Finish all the "Photo" quests in adventure mode
Finish all the "Jet Ski" quests in adventure mode
Finish all the "Treasure Hunt" quests in adventure mode
Finish all the "Feeding" quests in adventure mode
Finish all the “Collection" quests in adventure mode
Finish adventure mode with Maureen
Finish adventure mode with Wendy
Unlock all the outfits for Maureen, Wendy, and their friends
Unlock all the hairdos and hats for Maureen and Wendy
Ride 26 miles on a scooter and/or a skateboard
Mow 40% of the grass in "The Crazy Lawnmower"
Win with a score of at least eight points in "Claw Crane"
Win without falling more than two times in "Mud Pit"
Bring seven of the dogs back to your pen in "Doggies This Way"
Win without dropping glass in "Round for Everyone"
Win with a score of at least 10 points in "End-of-Year Dance"
Win without getting any penalties in "Mega Penalty Kicks"
Win by pushing at least two opponents into the water in "The Cracked Island"
Hit your stake five times in a row first in "Hit Your Stake"
Paint at least 50% of the wall in "Dominant Color"
Win with a total of at least 4 bowls in "Bulk Chocolate"
Win a match without making a single mistake in "Hungry Little Monsters"
Don't let more than ten balls pass by in "Extreme Ping-Pong."
Win by hitting at least four special targets in "Unicorn Toss"
Win with at least four special trash cans in "Trash Challenge"
Win with less than 5% of the toys in "Express Cleaning"
Win by filling at least four special crates in "Mayhem at the Market"
Win "Tag!" without being tagged
Prepare seven recipes in the allotted time on hard mode in "Cupcake Factory"
Finish the race without hitting the wrong button in "Triple Gallop"
Make at least 25 fries in "The Fries"
Hold for 20 seconds in "The Crazy Chandelier"
Win "Mind-Boggling" on hard mode
Win the "Whatever Race" with all the characters in the game
Win the All or Nothing mode with at least 20 points