I was looking for something specific to his assertions that you disagreed with. And the link lists 64 references, not one study.
The twin studies are pretty straight forward. 10 - 15% of individual identical twins who are attracted to the same sex, have a twin who is also attracted to the same sex. Which means 85% to 90% do not. Identical twins with identical genetics and societal influences can still make different choices.
64 references not all to studies and how many of the studies referenced actually agree with the author and are not just something he cherry picked? One study is often preferable as a source but just as a start.
But let's just start with the first few references in the pdf you linked.
Measurement models for sexual orientation in a community twin sample
http://www.ncbi.nlm.nih.gov/pubmed/11206089
Multivariate structural equation modeling techniques have been applied to examine the causes of individual differences in responses to several items concerning sexual orientation. To minimize potential ascertainment and response biases, the study sample involved a large (N = 4901) community-based cohort of Australian twins aged 18-52 who answered an anonymous questionnaire on sexual behavior and attitudes. The statistical power of the analysis was increased by the availability of multiple measures of sexual orientation (behaviors, attitudes and feelings),
providing stronger evidence for the existence of additive genetic influences on this phenotype than in a previous analysis (Bailey et al., 2000). Estimates of the heritability of homosexuality in this sample ranged between 50 and 60% in females but were significantly lower (heritability of approximately 30%) in males.
The second reference is to a book...
Homosexuality: The Use of Scientific Research in the Church's Moral Debate
http://www.amazon.com/Homosexuality-Scientific-Research-Churchs-Debate/dp/0830815678
For the third one see the note above on the first study.
http://www.ncbi.nlm.nih.gov/pubmed/10743878
Bailey JM, Dunne MP, Martin NG. 2000 Genetic and Environmental influences on sexual orientation and its correlates in an Australian twin
We recruited twins systematically from the Australian Twin Registry and assessed their sexual orientation and 2 related traits: childhood gender nonconformity and continuous gender identity. Men and women differed in their distributions of sexual orientation, with women more likely to have slight-to-moderate degrees of homosexual attraction, and men more likely to have high degrees of homosexual attraction. Twin concordances for nonheterosexual orientation were lower than in prior studies. Univariate analyses showed that familial factors were important for all traits, but were less successful in distinguishing genetic from shared environmental influences. Only childhood gender nonconformity was significantly heritable for both men and women. Multivariate analyses suggested that the causal architecture differed between men and women, and, for women, provided
significant evidence for the importance of genetic factors to the traits' covariation.