Fellow bisexual here -- I had this same experience with my own parents!
It can be *so* frustrating when you can feel that people around you are invalidating your sexuality, even quietly.
It makes total
sense that this would upset you. I understand the temptation to compare your struggle to others', but I promise you that what you're going through is valid.
I definitely have a few favorite ways of coping with this kind of experience. First, do you have any bi/pan/queer community spaces that you belong to? Friends at home, online, etc? Having community to vent to who understand what you're experiencing can be really healing.
Second, do you have access to therapy/counseling? When the people around you invalidate your reality, it can be hard to feel grounded in your truth. Having a professional around to affirm that truth can be really helpful.
If not the ones I mentioned above, what coping skills are you currently using, even if they feel like they're falling short?