Unfortunately, as you already know, if your mother isn't willing to help train them while she's watching them it's not going to work.
A dog doesn't know the difference between why it's ok to pee here one day but not the next(which is what is happening when you're gone and then come home). It sounds like you need to train your mother not your puppies
Is she living with you or are you living with her?
Your mom sounds similar to my mom(whose own pets are not consistantly housebroken). Not to offend but is there any chance your mom might have a slight mental problem? I only ask because my mother does. Normal people do not think it's ok for an animal to poop and pee on their beds, carpets or anywhere in their home. That is why I ask. She's letting them go anywhere in the house because she thinks it's cruel to keep them in a playpen but yet won't let them outside to go to the bathroom. You will need to point out to her it's ruining the home and is unsanitary. You will not be able to train them if she doesn't either let them out during the day or keep the wee wee pads where they can get to them. I wish you all the luck.