Not exactly sure what there is to be jealous about here.

move out.get better parents.

Well it does look that way a little bit. I would say drop the subject for now and try again later. Or since you technically already told them, you don't have anything to worry about really. You already know they won't react negatively. Maybe get your brother to team up to tell them again about you. That way he can lead the wave of support and they can't claim you're thunder stealing.

Fear of something similar happening is why I haven't came out to my parents

hi

Yes, because coming out as being part of a demographic that is at very high risk of being harassed, physically beaten, sexually assaulted, and murdered is definitely stealing someone else's thunder. Sorry that your parents are jerkasses OP- you can alway wait a bit and then come out again, or ask your brother for support on calling them out on playing favorites. You could also do as was suggested above and consider that your coming out even though they didn't believe you, but the fact you came out to them implies you want their support and thus need to get them to believe you. An idea that you could run by your brother would be for the two of you to throw a coming out party, and maybe put a little more emphasis on your part of the party- that way your parents PROBABLY won't be dumb enough to accuse you of trying to steal your brother's thunder.