Too, first thing to say is please please don't give yourself such a hard time with all the self hate. Really, I mean it!! If I were your friend in RL I would want to give you a big hug and tell you not to be so unhappy about things, or about yourself, be kind to yourself!! However I encourage you to start making small incremental changes, not massive unrealistic ones.
They say it takes 30 days to make a habit, so try to set yourself a few easy and realistic goals regarding portion sizes and type of foods to enjoy, then over time as you start to feel the benefits of success, it will encourage you. A special plate, or just a smaller plate can really help. Also drink plenty of water, stay well hydrated! And get into moderate exercise, again keep it realistic, enjoyable and build it into your daily commitments around the family i.e. a 30 min brisk purposeful walk which is ultimately do-able for most people can boost your morale - have it as you-time not just a random walk, see it as part of your new regime, keep it going regularly and notice the difference. Or a cycle, or a swim, something you enjoy!
Honestly there is no magic formula, start to think about food differently, not as something to ration or reward, but as something to keep you feeling healthy and fit. Also something to enjoy not feel guilty about.
I have been 9 stone 6 lbs most of my adult life, so I am hopefully one of the people who you mention in your OP as um normal (I don't know about that lol). Food to me is part of life, enjoyable, but not something I make the focal point. I rarely eat by the clock, just because its 1pm for example, If I am not very hungry I will eat less. Sounds very obvious but its the way I perceive food. Equally, if I am hungry I will eat more, but will always stop before feeling stuffed, as I cant stand that bloated feeling. If your body gets back in tune with what it really needs, and you let it tell you, rather than you telling it (!) you will find that fullness becomes the signal to stop and you dont go over that threshold.