M.F.
Here's a good rule to remember:
They will eat if they are hungry.
They're at the age where it will seem like they barely eat enough to survive. You won't be satisfied with what they eat at a meal until they're going through a growth spurt, or until they're about 3 or 4 years old. Maybe you noticed the same thing with your older daughter?
At any rate, you're good to be looking in to solutions now, because now is when the foundation is laid for good table manners/eating habits and bad ones alike.
First off, the melt-down hour. At 4:00, it makes me wonder if they're napping well, or if they're getting an afternoon snack. Even if they're down to just one nap a day, you may still want to enforce an afternoon "rest" time where they're in their cribs or playpens with some quiet toys/activities. If you know the melt-down begins at 4, pre-empt it by starting their afternoon "break" or "rest" at 3:45. or load everyone in a wagon or stroller for a walk or trip to the park about that time.
As far as snacking, you should remember that toddlers really need to eat small amounts often. A nutritious snack around 3:00 might help. Maybe goldfish and a cheese stick, some yogurt, peanut butter on crackers, apple juice and a piece of fruit, etc.
Meal times -- here's what we do in our house (it took lots of persistence and consistency, but we finally crossed over to peaceful family meals):
I make sure that at least one item on the plate is something they will definitely eat. Put the food on the table. If fits or drama begin, we say, "This is family time. You may eat nicely with the family, or sit on your bed (or in the playpen) while the rest of us enjoy family time." If the behavior doesn't change, that's you cue that they've chosen to leave the table. Here's where your pack n plays will come in handy with twins. Plop them in a pack n play, placed out of sight, and potentially out of earshot, and finish your meal. Don't feel bad about a kid skipping a meal. She'll make up for it the next time it's meal or snack time (just be sure you don't over-compensate with snacks, or she'll make a meal out of them!). When we began enforcing "peaceful family meal time" our daughter missed a full days worth of meals, then got up for breakfast one morning and ate eggs, toast, yogurt and fruit. We went through it again another time, and when she finally decided she was hungry enough to eat, she actually ate asparagus and salmon.
You have no reason to feel guilty or worry as long as you are offering healthy snacks and meals at regular intervals.
Also, watch how much of their calories they're drinking. Milk is pretty filling, and juice has a lot of calories. If they're drinking a big cup of milk just before a meal, they're not going to be hungry, and will not likely sit for a meal