If they binky all the time, seem happy and flop over, it seems like they’re doing very well. If the babies were weaned by week 5, they will be fine without their mother since they have each other. 8 weeks is more ideal, but now that you have them, you have them.
Baby bunnies can be fed freely, meaning they themselves regulate how much food they eat. You just refill the pellet bowl when it’s been emptied. Hay and water should be available 24/7. This is what baby bunnies should be fed, unless they were used to getting vegs with their mum. If they have never had vegs, 12 weeks is a suitable age to introduce them.
You could start weighing them if you have kitchen scales. Then you note down their respective weights and make a weight curve that you can follow. That way you can keep close track of how they grow/increase in weight and you can see if one falls behind.
Do they look very skinny? Are their eyes clear?