Why only bring one crate? Can't he bring much more? He said it himself that his bag of holding wouldn't change its volume or weight no matter how much stuffs get put into it. One of the reasons why he didn't put the two girls in his bag of holding was because it would reduce the volume of his bag, so he was already prepared to bring a lot.
If he didn't have to bring a lot, then he could have brought the two girls. Bringing only one crate shouldn't be a problem for even a normal carrier, so it would be no problem for a superior carrier like MC even if the volume of his bag of holding shrunk. The more people he bring, the more people to handle whatever it is that's happening in the spirit world.
Put the two girls in, cross over (there shouldn't be any problem crossing over with only two past skills), then bring the girls out after crossing over and he would be able to use all his past skills again. If he for some reason need to bring back lots of luggage to the human world before the path is stable, he can leave the girls in the spirit world first.
Unless I forget something.