it depends on a few things:
1, what causes people to develop their sense of what is attractive/sexual and what is not? That doesn't just mean gay/straight, but all of the forms of sexual and romantic attraction.
For me, I think its (like most parts of us) a mixture of our genetics, hormones/exposure levels in the womb, and our early-year exposure.
(All 3 of which are out of our control, and mean that you don't choose who you are attracted to)
the reason for me thinking its a mix is:
1, there have been numerous studies that have been able to show correlation between homosexuality in adults and early-year child abuse. That's not to say that all gay people have been abused, of course not. But if these studies are true, then it shows that early-year exposure, when your brain is still growing and forming at such a quick rate.. can impact your sexual preferences as an adult.
2, Genetics obviously plays a factor, as it does in most things - but I don't think its entirely the cause, and I wonder how its passed on.
3, There have been studies done, which to my knowledge show some connections between hormones levels in the womb, and a childs sexuality and gender as they grow up.
All three of these make up the idiom you are 'born gay' and you don't 'choose to be gay' - the second one is 100% correct, the first is mostly correct.
If that's right, then depending on the ratio of the three components, your parents, in making up a significant part of your early years exposures, could influence your sexuality to some degree. BUT that doesn't mean that having gay parents would make you gay, we have no idea what type of early year experiences drive what time of attractions later in life, its plausable that more exposure to homosexuality at a very young age could have some impact (but it would be very very small, because it would be a single part of a small cause of what drives your sexuality).. but there is absolutely no way to know.
So lets say purely hypothetically that it turned out your sexuality was driven 60% by genetics, 25% by your development in the womb, 15% by your early-year-experiances. Of those early year experiances, lets say that 60% are caused by your parents. That would mean that roughly 8% of your sexual preferences could be influenced by your parents.. but even then, if those numbers were at all real, we would still have no idea which parental behaviors or triggers cause which sexuality to develop, so whilst you could conclude that parents can have a very small impact, you could never conclude that gay parents have an impact of causing gay children.
even if you carried out a long-term study, examining the rates of homosexual children in gay and straight families, your results would quickly be invalidated by the fact that it could just be that children in gay families are more likely to come out, rather than actually be gay.