You can try refining the spam filter. Several years ago I had to write a lengthy set of outlook rules at work. They went something like this
Emails from [certain addys]
or subject matter contains [fwd, singles, mortgage, christian, obama, c!alis, ...]
unless [from certain people not spammers]
send to trash
YOu could add something like
unless body contains [grandpa, grandma, aunt gertie, birthday]
That way, you filter out emails from the parents that don't contain any keywords that might indicate they're not spam. Should work better. Any emails that you still miss, oh well. It's 2013, time for the email fwdfwdfwd craze to die.
Requires a bit of up-front work, but is worth it for the reduction in annoyance.
(Apparently our IT dept has gotten much better as I haven't had to update these rules in a long time )