Consdering how easily Uncle Mario took in Ezio, Claudia and Maria, one can only assume he obviously doesn't hate his sister-in-law. So how about some Maria/Uncle Mario friendship fluff? Doesn't have to be romantic at all.

Just perhaps Maria thanking Mario and Mario admiring his baby brother Giovanni at how strong of a woman he married, and how with Maria's help, Ezio and Claudia grew up to be awesome badasses. 'Cause you can't tell me that their badass-ity only came from the Auditore side...