Steam family sharing cant make acount

[HarveyHsb]

my dad owns factorio on his steam account and we are in a steam family together which also allows me to play the game when he isn't.
I can mostly play the game fine but im unable to mod the game because that requires an factorio account which im unable to make since i don't own the game on my steam account
Im wondering if theres a way for me to make a factorio account or if i just have to also buy the game for my steam account