It's pretty difficult to train that many young dogs at once, and adding the new one to the mix isn't going to help things, either.
I've staggered mine to the point to where one was well housetrained before the next one joined the pack. The housetrained ones helped as much as I did with training the new one.
It sounds like there are too many people involved, as well. You have to be consistent with how you train. If you have to live with this many people who are opposed to the way you train them and you have to change your methods to pacify the humans, you've got a tough road ahead of you. Everyone needs to be on the same page...
Surely your mother isn't okay with them using the bathroom wherever and whenever they want???