I'm not blaming the grandparents, or the father (although there are questions to be asked about his involvement). We don't know the full story. People do have a right to refuse entry to their homes - we hear on here about people who don't get invited into friends' houses - and I would be most annoyed of anyone demanded entry to my house, although I often have people round by invitation. If she found her house too difficult to look after (whether because of having four babies, because of failing eyesight or her learning difficulties) she may have become defensive and not wanted people to see the mess.
What did the authorities know about the situation? I am the first to agree that if there is evidence of harm being done to children there should be intervention, but if there was none how would they know? A suspicion can be followed up, but if there is nothing to go on when they get there, persistently targeting the family would become harassment. It's easy to say after the event that children should come first (of course they should) but do we want to live in a world where people can burst into our homes uninvited? Also, how many social workers would we need to make that a possibility, and how would we pay for them? Arguably that sort of behaviour would deter social workers from entering the profession, as they would become more like the police.
The question of 'essential' shopping came up in lockdown, with people very keen to judge others for the contents of their baskets. What is essential to one person may not be to another. I would never see sprouts as essential, but there is an argument for all vegetables being necessary. Even things like wine might be essential to an alcoholic, but a luxury to others. None of us can judge that sort of thing. How different was it from the (non essential) night out the McCanns had? I know I'm banging on about that, but apart from the state of the house, the situation seems very similar to me. Something terrible happens to children who seem otherwise loved and cared for when the parent(s) were avoidably away from the scene. One family gets support, enormous levels of funding across Europe and sympathy, and the other is jailed for ten years.