I can so empathise, its a terrible situation to be in, and especially with two you must feel as though this has been going on forever and will never change. It will eventually... but in order to help it along, you've got to get yourself a strategy or two in place.
I found the grumpiness really didn't help, especially if it came out at bedtime. Although its totally understandable I think it helped to get us (everyone is different, so you can decide for yourself) into a vicious cyle. As a result, you need to try and figure out what might help you temporarily to feel slightly less worried and therefore grumpy in order to be able to break the cycle.
Is your partner able to help you out sometimes and give you A) a night off - wear earplugs and sleep on the couch or at a neighbors and B) an evening off, or taking control of one aspect of the bedtime routine so you aren't both having to do battle to convince them to brush teeth etc. as well as waking up?
For the 4 year old, a sticker chart with clear rewards after she's accrued enough stickers - going to a favorite place she likes or getting a new little toy she wants etc... can really help to motivate her to go to the bathroom on her own. If she's still struggling with the toilet, you could always put a potty in her room, and just empty it in the morning - giving her a gold star if she makes it through the night without getting you up. Explaining to her that everyone needs plenty of sleep to be healthy and smart and happy enough, and that if she and her brother can sleep it will benefit them as well as you can also be worth a try.
Also, i found that getting my nearly three year old a 'relaxation' tape from Amazon helped us all a lot - at least at first before he got bored of it. We'd both listen to it in his bedroom, me lying on the floor on the opposite side of the room, and him in his bed. I found it helped me to relax, and perhaps because I was more relaxed, then he was as well.
We're in the middle of getting my son into his own bed after nearly three years in ours (it was the only way we could cope with the sleep issue when he was little) so we do know what its like - total nightmare at times. It will improve if you can help yourself and them feel less stressed, and if you put in place some family strategies that you believe in and can stick to. Good luck!