If you are having to access historial medical records about your relative with supposed vaccine reaction, there is little reason to suppose that your baby will have enough genetic/heridatary similarity for it to matter.
On top of that, many vaccine reactions are not actually vaccine reactions - they are separate events that occur at approximately the same time and we ascribe correlation or even causation when none exists.
As others has mentioned, of the reported vaccine reactions, very few exhibit any proof of causation, and the few that do, and are serious, are often triggered, not caused by vaccination. Someone upthread mentioned triggering via fever which would have happened during the snotty toddler years anyway.
So unless your very close relative has an inconrovertibly proven vaccine reaction causing damage, you have no reason to opt out.
Anything other reason comes down to mental health - anxiety over personal experience (still struggling to understand how it can be so close to you but you are researching records?) -or anxiety from reading dodgy websites and being susceptible to popular I-know-better-than-the-immunologist-with-a-Phd-and-decades-of-peer-reviewed-evidence-and-meta-data-studies
Visit the GP and get some counselling to help you through the anxiety and paranoia, oh and get your whopping cough vaccine while you are there!