The plural of descendant is descendants.

no, its their descendants (future grandchildren) the loonatics are....

Ace Bunny.........Bugs Bunny's descendant

Lexi Bunny...........Lola Bunny or Honey Bunny's descendant (i think Lola)

Danger Duck...............Daffy Duck's descendant

Slam Tasmanian.........Taz's descendant

Tech Coyote...........Wile E Coyote's descendant

Rev Roadrunner..............Roadrunner's descendant

Electro J Fudd...........Elmer's descendant

Gosar................Gossamer's descendant

Trixie Duck.............Melissa or Tina's descendant (fan base)

Pinkster Pig................Porky and Petunia's descendant

Ophiuchus Sam..............Yosemite Sam's descendant

Queen Grannicus...........Granny or Floyd's descendant

Royal Tweetums............Tweety's descendant

Slythvester Cat.................Sylvester's descendant

My grandfather is my oldest living descendant.

The opposite of the noun descendant (offspring) would be ancestor or forebear.

The opposite of the adjective descendant is ascendant.

My great-grandfather is a descendant of a famous war hero.