Can phone (land) lines get crossed in one household (two seperate lines and two different telephone companies)

Wires crossed in the building. Doesn’t have anything to do with WIFI or different phone companies. Other companies still use AT&T (or babybell) lines to provide their service, if it isn’t over their co-ax.

I have both my land line and internet service through the cable company. When I answer our cordless phone, I get kicked off the internet. I used to be able to pick up a neighbor’s phone calls on their cordless phone on our baby monitor.

While this doesn’t exactly answer your question, I think that depending on the phone service, and the cordless phones, it’s entirely possible that the signals intercept.

Nope. 32 years of experience says it’s crossed lines.

I don’t have land line phone service anymore, but when I did I can remember things like that happening every once in a while. If you call your phone company they may be able to come fix it.