Would ningengumo (人間蜘蛛) be the correct term for a semifer (latin for half-beast) creature in japanese that would be half human, half spider? The closest term i can find is for a yokai called jorōgumo (絡新婦) which is "prostitute spider", but denotes a female only. I'm looking for a gender inclusive term that would mean a complete race.
The traditional pattern for this is
～娘 "-girl"). You can use 蜘蛛人間 or 蜘蛛男 to describe a character like Marvel's Spider-Man. For example, this episode list of Kamen Rider has many examples of monsters named ～男 (oh, the first episode is exactly about 蜘蛛男, which looks like this). 狼男 is the Japanese term for werewolves.
On the other hand,
人間～ usually means "human ～" or "human-simulated ～", and it has nothing to do with imaginary creatures. 人間椅子 (human chair), 人間盾 (human shield), 人間ジュークボックス (human jukebox), etc. 人間蜘蛛 makes no sense to me.
爆弾人間 ("bomberman") sounds like an imaginary bomber-human hybrid, whereas 人間爆弾 ("human bomb") refers to real people who attempt suicide terrorism.
Jorō-gumo is the name of a certain Japanese yokai, and you cannot use it to refer to other spider-human hybrids in general. In particular, Marvel's Spider-Girl is never called a jorō-gumo!
There are several fixed terms that do not follow the pattern above (e.g., 半魚人 "merman", 人魚 "mermaid", 半神 "demigod"), but they are not really productive, and you generally cannot coin a new word like these.