I've read all of your posts op and the first couple of pages.
Firstly, I don't think your food shopping is excessive in the slightest. The cars are mandatory.
I think the focus should be on the positives: your dh has a full-time job and is a grafter. His income is likely to increase £60pw after about 12 months. You have kept your hand in with a 12 hour a week job with the church, despite having three children.
Life is tough at present and feels a bit "jam tomorrow" but your dc have a stable family, grandparents on both sides, enough to eat and plentiful love.
This summer may feel a bit mizz when everyone else is being tone deaf but there's so much you can do with the dc who won't be consigned to three or four weeks at holiday club for the summer where they come home exhausted and little Johnnie has told them they're stupid. But you can have picnics, spot insects and keep and insect and plant diary, possibly get to the beach and look for shells and crabs, find a couple of activity days, crazy golf, etc. It will be nice.
Regarding other people, they either have more coming in, more practical help from parents or are bankrolled by parents. Alternatively they might have remortgaged in 2021, blown the extension money on a car and three holidays, including Disney and be bricking themselves about the future.
Focus on all you have and big it up to your DH. You are doing the hard yards.
Practically, can you network a bit at church where you are known? Could you offer some part/time admin, to help the elderly with a bit of cleaning/shopping or actually to offer to help the elderly for a small fee with IT related things, buying a new phone, using their Internet, or working out the TV? Honestly there must be a market when I think how my mother and MIL muddle through and you have trust by association through your work at the church. Can you start helping with the playgroup and perhaps pick up a bit of paid babysitting/cat feeding/dog walking, etc.
Good luck.