You CAN get humane traps, but those only work if you can empty the mouse at least a mile away from the house and you can get it fairly quickly after the trap being activated. I once went through 6 humane traps in three days because the mice got caught in the trap overnight and then chewed their way out.
They will breed though. 2 mice quickly becomes 20! The only way of getting rid of them effectively is either to get a cat or to poison them. Your mum is unfortunately, going to have to make the choice between killing them or living with them if the humane trap solution does not work.