No, you do not need to join the same Medicare Part D prescription drug plan (PDP) as your spouse. Medicare covers individuals — it does not jointly cover husband and wife like some employer-provided plans.
There is no financial advantage for spouses to enroll in the same plan. You and your spouse may have very different health conditions and medication needs that could require specific types of coverage. While you may be able to help each other in the selection process, always consider your individual needs when choosing a plan.