I have read the whole thread. Here are my thoughts for things you might want to think about.
Breastfeeding toddler -not a prob. Lovely that they are comforted by it. They might get quite a lot of calories from breast milk and that's not a problem. It's good for them. It does mean that the complementary foods they do eat should be energy dense and nutritious. Less focus on fruit.
Think about about cutting out juice and sticking with water/breast milk for both children. Juice is not nutritionally helpful really.
Hard to tell the amounts you are offering from the thread. Have you thought about keeping a diary for your own help in working it out including actual amounts?
A few mouthfuls could in fact be enough, depending on what it is. Just fruit for a meal or snack isn't nutritionally complete enough. Loads of suggestions in the two links I posted. You need to include protein and fat in each snack/meal, e.g. Cheese/full fat dairy, hummus, meat, nut butter etc. Vegetables are better than fruit generally nutritionally. Avoid flavoured/fruit yogurts, and stick to plain full fat.
Small regular meals snacks are better at that age, so e.g. Three meals and two snacks plus supper. Food every 2-3hrs in small amounts.
How active are they? They should be moving a lot. If they are not hungry enough to eat the above could they walk/cycle/scoot more? It is very easy when you are busy to not realise how little they are moving, even though you are (e.g. Younger child in buggy/sling, but you walking).
Your kids might be eating enough in calories, but you perceive it as picking because your expectation is that they will eat more. Or they might be eating enough, because they are not very active. Or they might be eating enough, but not of the best balance of things, or they might not. It is v hard to tell from this thread.
If you are worried, you could talk to the HV or GP.