They can only enter if you leave a window or door open for them to enter.
If they break-in that is a criminal offence and the police will treat it as a buglary and arrest those in the property.
I used to squat here on Airstrip One in my twenties when I was homeless.
We did not squat in homes where people lived, We squatted in empty properties.
The utilities companies would reconnect the gas and electricy for us but only if we paid a substantial deposit.
I dont see anything wrong with squatting in empty homes.
It is the fault of society that creates homelessness and squatting is sometimes the only way to get a roof over your head.