Network ipad problems?

My son has the triple play with Comcast and his wireless laptop works fine, but his wife’s ipad and iphone have trouble connecting from time to time, her ipad will not even let her join our own network, when she see her wireless network and clicks on it to join it it comes back unable to connect even though she connected the day before. It won’t ask for her password to join. We tried rebooting the modem but it has a battery backup and we worry about bring down the T.V. and phone system. Thanks Jim