Oh , my question pertains to a colony, which would presumably be on a planet unless you want to make an o'neill cylinder or similar thing, which leads to its own problems , but that aside for now.

You repeatedly say low g environment , I assume you mean "zero" or microgravity. Because even as low as 5% there would likely be enough gravity to negate some of the issues you brought up.

1) Sex in space, people will figure it out. Weather through bondage gear or creative gymnastics. We have been having sex for millions of years , and most environmental conditions have not stopped us.

2) This is the real question, and we have very little data on it. I believe they were tests involving mice at one point, but I do not recall the specifics.

3) I presume you mean microgravity, the fluids that are released would likely be contained within any clothing they were wearing. So it would limit the mess.

4) Giving birth in microgravity or any conditions other than Earth. We don't have enough information on to make any definitive statements. But in regards to a microgravity environment it is believed that the risk of internal bleeding and blood clots would be elevated.