Talk about eating your cake and having it too. You want to leave the somali gene pool, but also feel like you're passing something on. Truth is, you leave, you leave. That's the end of it. And culture is tied to groups of people, it's foolish to say otherwise.
You think the descendants of Italian/Somali couples from the colonial days retained any of their heritage down the line in Italy? Nope, they assimilated into Italian culture. And today, the descendants of that first Somali/Italian wave look and act fully Italian.
Why would your ajbabi grandkids practice a culture that is tied to a specific group of people they look nothing like? Why wouldn't they simply identify with the culture that matches their own phenotype and surroundings? You're being unreasonable.