Remember that one time you heard a story about a child that was "turned gay" because his parents were gay? You don't? Of course not. Because that's not a real thing. You can't "turn" someone gay by being gay yourself and being around them. Just like you can't "turn" someone straight by being straight. Sexuality isn't contagious. Who you fall in love with or who you develop feelings with, regardless of gender, is not a choice. It's involuntary. So please, stop worrying about the parenting skills of people that clearly have no issues in raising their children, and worry about your own.
Gay parents and bisexual parents are just like straight parents. They're human. They love each other. They love their children. Their parenting skills are the same as any other parents'. If anything, having same-sex parents would hopefully be more mind-opening for the children: instead of telling them that loving someone with the same physical parts as you is wrong, they show them that love is love and it shouldn't be frowned upon. Of course, I'm not saying that all gay parents can't be bad parents; that would just be inaccurate. Gay parents can be bad parents just like straight parents can be. Not everyone is perfect or makes the best decisions.
I fully believe that your sexuality is determined well before you even know what it means to like someone. I believe you're born with it. One might not be aware of their sexuality until they experience an emotional, physical or mental connection with another person, but it's still predetermined. People shouldn't be looked down on for something they have no control over. It shouldn't matter what other people prefer, because it has no affect on another individual. So let gay parents raise their kids and you raise your own. They're doing nothing wrong by being themselves. Their sexuality doesn't affect their ability to raise children nor does it affect the preferences of the children. Because again, sexuality is not a choice. If you think it is and you're straight, I dare you to choose to make yourself aroused when looking at pictures of the same sex. Because if you can, you didn't prove me wrong, you just proved you are, in fact, bisexual.