I know this is a really hard time - the first couple of months after diagnosis are so awful. So much shock, so hard to accept the reality of what has been pronounced.
It's a hard time of year for everyone as well being such a 'festive' season. Many people are on holidays or at least things are not running as usual.
It won't change anything if you just slow down a little and see if you can contact the cousin's spouse personally. Is this a first cousin, or a more distant relative? I only ask because you said
I just need to make some more calls to family members and see if anyone is still in touch with the cousin's spouse.
I say it won't change anything because it's not like this would open a treatment option. It could make a difference if you are interested in trials for particular genes, but again if it takes a couple of weeks that is not going to make a big difference.
If this is a large family, it would normally be known that it is FALS because there would be more than one person that has been affected. Our Nikki for example (who is away at present) is the 6th person in her family in her own life time. That is normally how FALS goes.
It is worth pursuing, but if this is not a first cousin, and there are no other family members affected, it is unlikely to be FALS. If you can't find the cousins CALS, and again, if this is not a first cousin, you are unlikely to access records, and they may not be a big deal. If this family member was the first in the family to be diagnosed, then it is unlikely that any genetic testing was done as they would not have been looking for FALS.
I can't imagine how distressing it could be to feel that on top of this diagnosis you are dealing with FALS, but I hope you can just let yourself breathe a little, and see what the family can turn up.