Babysitter - Full-time / Part-time

We have 3-month-old twins, a boy and a girl and need help with them a few hours a day. Someone to watch them, change their diapers, bottle feed them, console them, and help put them to sleep for naps. They are generally not too fussy babies, it's just that two at a time is a lot. Dad works from home, and Mom will be around a lot of the time too. We have a 4-year-old too, but she is starting full time pre-school mid August. We also have a German Shepard dog, who is big, but very sweet and safe.