Basically, I want to be able to add cum at the end dripping out of the girl's pussies x////x; I assume it'd be an MME effect.
you can use selflotion or fluidsimulation for that
and you can use cum models and animate it your self
I assume that flowing semen is MMD models, not MME effects.
The SelfLotion MME will only have absolutely straight threads pointing right downwards. And SelfLotion will go straight down inside models and out of models further down. So it won't look credible as semen.
The FluidSimulation MME doesn't seem to allow fluids to flow at lower rates than Null_13=1.1% at 30 fps. And 1.1% flow is too rapid and thin to look credible as semen, as you can see in the end of this video: https://ecchi.iwara.tv/videos/lyz8qsozqf85qq3a
I think you need to get hold of good semen MMD models? And once you have them, you'll probably need to update the positions and angles of the bones inside the semen models frame by frame, to make the models move as you like?