Can girls visit the kever of zaddik ribnits at nightime with other ladies present in ohel? And with the men in their section?
Without getting into the issue if girls should be visiting a kever of not, my understanding of your question is if there is a yichud issue. If there are more than two girls there, or if there are two men there it would not be yichud. Even though it is nighttime and at night there is a need for an extra person, however that is only in a place that someone might go to sleep, and I don’t think that this would be happening at a kever. Additionally if it is at a time when there are frequent visitors to the kever it wouldn’t be yichud because a different person may come inside
Shulchan Aruch Even Haezer 22-2.