I have 3 chihuahuas and I keep them in a small area next to the kitchen when we don't have the time to be with them. I use a baby gate so that they can see me when I am in the kitchen so they don't feel alone.
I find that chi's, especially until they are very well trained do not do well when they have the run of the house. It gives them too many options to go potty and they really don't see the difference from grass and carpet.
The chihuahuas may also miss your mother. Chi's get very attached to one family member as it is and these have been uprooted and have no idea what is going on. Be patient and CONSISTANT.
Remember to only feed them at certain times of the day and then put the food up. It is hard to potty train them when they have to go almost every time they eat and the food is left out. Put their water dish up after 8 or 9 at night.
they are creature of habit so just keep it consistant and they will catch on.
God bless them, they are adorable.
My three