English is not my native language and maybe I see things differently but those lines are not talking about summoning both genders. One is for summoning female and the other is about summoning male.
"Barbed Collar of the Succubus - Strengthen your pact with your Succubus, ensuring that your ritual will only summon them."
"Barbed Collar of the Incubus - Strengthen your pact with your Incubus, ensuring that your ritual will only summon them."
Succubus is for me female, and female for me its "her" not "them".
Incubus is for me male, and for me its "him" not "them".
But it's better to be safe, someone could get angry and offended right