Hi and welcome,
Having a genetic susceptibility with MS is typically from a closer relationship than cousin's ie mother, father, brother, sister, the further removed from your genetic pool the lower the susceptibility. Having cousin's with MS is suppose to be even less than if it was an aunt or uncle.
Unfortunately, though having said that, the small lesion anteriorly at the calloso-septal interface would place MS quite high on your list of possible causes because of that specific location having a higher association....
"A recent study [1] showed that lesions at the callosal-sept-tal interface (CSI) demonstrated by magnetic resonance imaging (MRI) were a sensitive (93 %) and highly specific (97 %) indicator of multiple sclerosis (MS)."
https://link.springer.com/article/10.1007/BF00588395
.....and one of the reasons why the radiologist states in his conclusion "Cerebral appearance highly suggestive of demyelination"
The diagnostic process can be stressful and take a long time, MS is diagnosed on a lot more than just the MRI evidence, there is some MRI evidence suggestive of MS but until all your test results are in, it's in your best interest to try to stay open minded to what might be going on.
I hope that helps......JJ