Absolutely possible. Fraternal twins, with parents of different ethnicities. One twin took got more similar genetics of the mother, the other of the father.
(Probability and genetics/genetic disorders is super interesting and weird. I want to get my masters in genetics.)
I've heard about something like this. The mom had a boyfriend who was white, they had sex, she went to a party the same day and got drunk, had sex with a black guy and so the twins ended up half brothers.
I read about something like that in one of my biology classes. I also read about a woman who had fungus growing out of her throat that eventually filled her mouth and killed her. Science is fun.
(Probability and genetics/genetic disorders is super interesting and weird. I want to get my masters in genetics.)