Your kids are at difficult ages. The 18 month old is just a big baby (in that he/she has the mental understanding of a baby, but the abilities of an older kid). It's easy for people to think more should be expected of them.
I would hate being in your situation. Figuring out parenting is hard enough on your own, then add your parents who make you feel constantly critiqued and judged for what you do - no thank you!
I'm confused as to why they call you freeloaders and then let you live with them. Isn't that enabling you? (which I don't think you are freeloading!) If they expected you to pay for rent, they should have mentioned it. Or if they want you to now, they should let you know they want rent. They shouldn't call you anything if they are approving of the situation by their actions (by letting you live there).
I personally wouldn't put my kids in daycare to get a job. I'd move back with my hubby first. I don't know if that's an option. But it would resolve a LOT of the issues you're having with your parents.
I would consider having a sit down chat with your parents and explaining that when they are criticizing you, it doesn't help the situation. You are a new mom and you are doing the best you can do and that you're learning as you go along. You appreciate their desire to help when it comes to the kids, but it's not helping.
I'd try to just let them know to stop it. I've found myself in the same situation. When I have family over, I feel like they are watching and judging. I know they are! They do it with other family members. And they are so critical. Funny thing is, the main one that does it only has one child...and somehow that makes her an expert on how to handle 4-5 kids in a family? The dynamics in a larger family are so different! But, I find myself getting upset at the kids easier when I have family around that I feel is watching and judging. I feel really on edge and like she's judging everything I do. She often doesn't flat out say anything, but she'll sometimes make little comments here and there. People EVERYWHERE seem to do it. They've done it to me, to my friends, to my family, etc. Everyone seems to know better than everyone else on how to raise kids. That's why I think it makes sense to leave it to the parents and stay out of it!
They should be leaving you alone. If it affects them, then they need to figure out how to discuss boundaries with you (such as kids not going into certain parts of the house or not touching certain things, etc).
and, you need to do some soul searching, figure out what type of parenting you want to follow, and stick to it with confidence. Don't let their criticizing and judgement change how you react to things...don't let it make you angry and yell. Your babies are too little! (and, I don't say this meanly - I TOTALLY understand why you do that. I've felt similarly before too.)
It's a rough situation. Something definitely needs to happen! good luck.