Welcome to the chaos of having kids so close in age. I have the same in age as yours, 5,4,2 but add 1 and almost cooked to the list too.
My partner and I have household responsibilities each. He the kitchen and cooking, me the laundry. The rest gets done when we get to it. You could try this in your home.
We also don't give in to our kids demands. If they push things too far, they get sent to the timeout corner. All your children are old enough to try this now. Ignore the tantrums and just keep putting them there until they start behaving how you want them to behave.
I'm guessing with your 5 year old she is in school by now. Yeah, we got miss bossy britches here too. She is an angel at school, but at home, well, lets just say the halo slips and she thinks the is the boss. She is the one who spends the most time in the corner, but still isn't getting the message.
ADD and ADHD are too readily diagnosed these days. Drs just go with what you are saying without really assessing the child properly. I had a friend who's parents just took her to the dr and demanded she be put on medication. She was worse on the meds than off it, so didn't need them at all.
These disorders are characterised by lack of attention to anything. That is, they can't focus on a task for more than a few minutes at a time. ADHD includes the child not being able to sit still, and I have heard that children with this will sleep fidget too.
Thankfully for us, ours don't have either, though they are pretty boisterous and highly energetic, but they focus on tasks and learn new things very quickly.
Your oldest needs to learn to do things for herself. If she doesn't start taking some responsibility now, then she will be a very difficult teen to deal with. Try getting her to make her bed, put her dirty washing in the basket, and other simple tasks. Create a rewards chart where she earns toys, books or other special rewards. This should help her with goal setting too.
I do have to ask about your relationship with your husband. If things aren't good between the two of you, then this is going to have a big impact on the way your children behave and the way they form friendships too. A marriage takes work from both partners, not just the wife, so you both might need to work on it together, getting marriage counselling to help you along.