You realise that you can't do this alone. You can have your own DNA tested till you're blue in the face but it's worthless unless you can persuade your parents to have their DNA tested too.
But I have to say that your reasons for thinking they aren't your real parents are insubstantial to say the least. There is no connection between someone's 'interests' and their biological connection to another person with different interests. Countless children grow up without ever establishing a common interest with either of their parents.
Conversely, you could be adopted, and find that your adoptive parents share ALL your interests. It is a matter of chance, NOT biology.
As for speaking Arabic, there could be a dozen reasons for this, not one of which you've addressed. Your biological connection to your parents does not determine what languages you speak; language comes from what you hear around you every day, so for example if your parents never speak to you and you have only a Spanish tutor for company, you'll learn Spanish.