TDap in family members

So when I got my TDap shot my OB recommended anyone that will spend a bunch of time with baby get theirs. Talked to my family and they understood, talked to my in laws and since they had it many years ago they think they are good. Is it bad I want them to get it again? On a side note I got the shot when younger and had whooping cough in college and the doctor told me then the vaccine wears off over time. I have told my husband this since he is on his parents side so now I will be asking my OB at my next appointment but just wanted thoughts on this.