As long as your girls get along well I think they'll be fine. I assume they know the rules about answering the door? They know your cell number? Do you have an alarm system you can turn on? My oldest is 10. Very mature. Very responsible. He will stay home while I drop off his brother (about 15 minutes round trip) every week. He has stayed home while I grocery shop. I have not left him home with his brother(s) at all. My younger two are too unpredictable for that. But if they are both relatively responsible on their own (I think they are both old enough to stay alone)...I don't see the issue.
Mama to my boys (04,07,11)