If my twin brother has hemophilia but I don't, what are the chances that my kids will develop it?

Depends on sex. If the unaffected twin is male he would not carry the gene and could not pass it on to his children. If the unaffected twin was female she could be a carrier and could pass the gene on to her children. If she did her male children would be affected and her female children would be carriers.
High for your sons. It seems like you are a carrier, since your brother twin have disease. The hemophilia is linked to x-chromosome, so 1/2 of your sons will develop it, if you husband is healthy.