I've got a question/need advice about how to handle a situation with my mil and her twin sister. This may be long, so I apologize in advance

Ok, so to start, my husbands aunt (his mother's twin sister) had a baby 35 years ago that passed away of SIDS at 2 months old. His aunt and mother blame an allergic reaction to the pertussis vaccine. They questioned several doctors about this and they all told them that unfortunately there is no explanation.
Fast forward to now, my husband's aunt now has two adult children, neither of which have had the vaccine. Her son has several health issues such as epilepsy and many other things(I only include this because the baby that passed was a boy as well). My husband has also not had the vaccine because his mother always said that he was allergic to it. My husband has two uncles who all have children who have had the vaccine and have had no problems.
His mother and aunt have now been bringing up us giving the vaccine to our little one. We have spoken to our OB and the pediatrician who have assured us that a fatal pertussis reaction is HIGHLY unlikely. His aunt calls at least once a week from Texas to talk about this, and to insist that we not give the vaccine to the baby. I did get the vaccine two weeks ago and LO is still healthy as can be inside of me. My husband isn't sure how to go about this sensitive subject either. Understandably, his aunt and mother are still very hurt and upset about her baby passing which I totally understand because I would too.
Any suggestions on how to talk about this subject with them? And has anyone had any experience or advice on giving the baby the immunization or not given this stiuation? In my opinion the baby should absolutely get the vaccine.
Re: Pertussis Question- Loss mentioned
I would certainly still have the baby vaccinated. I would try to be as sensitive as possible but let them know you discussed it with your OB and pediatrician and they assured you LO will be safe.
Other than that I'm not sure what you can say that will convince them. Just explain that you feel very strongly about it and you are confident the risks or not vaccinating outweigh the risks of doing so.
as for how to handle mil and aunt...do they really need to know??? I mean, you can listen with an empathetic ear but it doesn't mean you will take their advice as gospel every time. I wouldn't even tell them.
ETA: In fact, the reality that their side of the family has refused to get vaccinated against pertussis makes it all the more important that you get the baby vaccinated as soon as possible, and that you limit their contact with the baby until that point. They could very easily act as carriers for it, since they have no current immunity to it. That your husband isn't vaccinated is more worrying still.
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Yep. I look at medical records all day long and I've never seen one given that wasn't the combo.
Not necessarily. An adult "tetanus booster" is usually just Td. You have to specifically ask for the Tdap.
Learn something new every day, but that makes sense for people who keep up with vaccines that a booster wouldn't be the whole schbang. I wonder if they gave OP's MIL the option of the combo or the other. But from what I've read in records if a person hasn't had a DTaP in 10+ years they stick them with the combo.
@DSMLove: thank you!