NPHC GLOs are a big part of my family so I didn't and don't have to explain to my parents. They love NPHC GLOs, certain BGLOs in particular.
Your situation is complex because you have West African and religious concerns. My biggest advice is to show them the good your GLO does in the community and world. Have your parents read something and invite them to a service event. Your parents will still see the negatives including the websites of ex-members who say BGLOs are devil worship. They will decide to what to give the most credence.
Now that you're grown there may come a time when you keep certain things separate from your parents. It doesn't mean you love your parents any less and doesn't mean you don't respect your West African and Christian roots. It means you are an individual who has figured out/is figuring out what makes you happy. That isn't easy but you will see what works for you. That is even less difficult if you are paying your own GLO dues and overall bills.

Good luck.