My dad asked me permission to marry his girlfriend?

My mom passed away 4 years ago caused brain cancer. I live abroad with my fiancé. But my dad live with my sisters. Last month when I visited them my sister told me that my dad has girlfriend and they don’t like my dad’s girlfriend. Coz she is from poor family and her 1 son work as construction worker and the other is Janitor in my sister office. My sisters think what my dad has now is because of my mother's hard work too, she helped my dad from 0 until he has everything and got rich. And my sister don’t want other woman just enjoy it now.

My dad told me that she wanted to introduce his girlfriend to me, but i told him
“Better you choose a woman who same as us, same education, same level and everything. If you want to get married, of course u can, I understand that. But I don’t want to have a poor woman as my stepmother”. Am i too selfish? I feel bad to my dad, i know he is lonely, need someone to accompany him, but i also think my sisters are right.
My dad asked me permission to marry his girlfriend?
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