House Trained Dog Peeing and Pooping Inside?

My dog is neutered and he's five going on six years old now and he's been potty trained since he was one. We just moved like a few months ago and he was fine with it, because he went from a condo to a big house. We also just had a new husband and kids added about is year ago, the two new kids are only here every other week, but the other two he's been living with are always here.

Now sometimes when we leave, he pees and poops in the basement! Even if we have only been gone five minutes (we never leave for more than an hour without him). I am almost forced to get rid of him! Whats wrong with him so I can try to fix it?

By Bailey R.