Neither of these characters is named onscreen, and since they are both played by the same actress (Bobbie Brown) as the same kind of eye candy, here they are together.
Nibbles appears in "You Better Shop Around", both parts, as the girl both Al and Bud strive mightly to persuade to bend over and pick things up. When the Bundys seem to have won the "million customer" shopping spree, Al grabs her and drags her into the family group hug. He proceeds to check her heartbeat instead of Peg's, scratching her with his ear hair in the process.
Pecan is one of the 'rewards' (all seemingly named for types of nut) Al envisions himself acquiring with the gold he's found in "Route 666 (Part II)".