Are all xenomorphs female

Answer 1

Nobody is 100% sure, but they probably are. Basically any Xeno can become a Queen. They only Xenos that are (possibly) male are the genetically modified ones, such as the Rogue. However, the gender might be determined by the gender of the host, since the developing Chestburster often combines the host's DNA with its own. It's really hard to say for sure.

Hope the insane complexity helps! =P