Inside the vagina. The sperm swim rapidly to the uterus through the cervix.
No, because the risk is to high and they should keep it private.
One way unequal power relations contribute to the spread of HIV infection is because of forced sex or non-consensual sex and if the partner has any kind of STD (which is probable since most are with more than one person).
Sorry if this is written weird, I'm only in 9th grade so I don't really know this much about it. Any who, hope this helps!