The link was already supplied, on this page, to this
post but to basically repeat verbatim:
You need to open the file */ProjectR_Data/StreamingAssets/Character/woman(or/sister)
You open the woman0.character file or sister.character file (use something like notepad)
You replace the "Type":"Slave" with "Type":"Monmusu"
As I haven't done it personally, I don't know if that shuts off Goblin sex, but animations exist for the characters to enter combat. Unlike having sex, which the shortstack does not have animations for.