Mom didn't give them much of a gift. But the brother and sisters didn't grieve for long. The Asian girl took advantage of the moment and coaxed her sister into talking her brother into a threesome. Considering that the Asian girl has a petite physique, it looks like an elephant and a moose against her brother's big dick.
And why the girlfriend was so turned on - he was her half-brother, not her own. And who's gonna train his sister, a stranger's uncle? No, only your own should be trusted with her pussy.