Plant 5 plant pots in one game of Garden Ops or Gardens & Graveyards.
Difficulty: Extremely easy
Cousins can easily be earned in Gardens & Graveyards, as zombies will often vanquish recently placed plant pots, so you can plant it again.
In Garden Ops, this is very easy if you play a solo game. If you are playing Garden Ops with other players, run around to the nearest plant pots and plant your plants before them. Less players try to plant in pots far away from the garden.