Albert Steptoe is amongst his other traits an habitual humbug, by his time in life he has got used to having everything his own way, this includes the annual 'family holiday', expecting to be able to continue indefinitely.
Albert is typically bitching about son Harold's exotic foreign holiday because he felt excluded, but when when Harold's best laid plans go awry he is all too keen, to be able to profit from it at his expense.
In my own home family holidays were while us kids were at school, in that generation kids were happy to leave home and stand on their feet as soon as they were able to, so by Harold's age most sons would have been long gone.
It's no wonder that he had left home to join the army, a very common practice at that time but not that many sons, would have come back to the same environs on being demobbed.
But Harold was stupid enough to risk it and then lived with that mistake, for the remainder of his unnatural existence.