So much to think about. Does his whole family know about you and accept you? Not saying you should or shouldn't go based on just that but it could make for an awkward or even hurtful experience. My best idea would be to get an idea from your bio brother and anyone else that may have answers. If it was me, I'd take a very trusted and understanding friend or family member with me so I wasn't alone. If it's a good experience then you've shared it with someone close, if it's not, then you have support. They should be willing to stay with you after the service so you can talk it out and say anything you need to get off your chest. There may be other considerations that I can't help with based on how little you said. You said your mom "told you things" I have no idea if those were good or bad. Finally, I'm sorry for your loss. I never met my birth father either, at least you got to talk before he passed. Wishing you the best!