Flu shot opinions

My son is 12 weeks old. My husband and I got the flu shot, and so did my parents because we are living with them for the time being and they help with the baby a lot. My mother in law and sister in law hold him frequently and have been kissing his cheeks and cuddling his face but they refuse to get the flu shot. My mother in law did get the TDap, but I just wondered if I should be pressing the issue of them getting the flu shot if they're going to be so close to his face. They generally see him once a week. I'm not big on shots--I haven't ever gotten the flu shot til this year and I'm a teacher--but I also don't want my baby getting sick. I'm a FTM, so I just don't know how worried I should be about it.