Please help! Our relationship is like walking on eggshells!!!?

the kid seems to be a brat. as a family unit, there needs to be rules and mutual respect for those rules. It isn't about eating all the cereal or wearing something of someone else. It is the inconsiderateness of not being cognizant that others will want cereal, so don't eat it all. Or asking to borrow clothes. Again, it is plain and simple, the kids are not respectful. It is up to their father - and you with his support - to set the rules of what is appropriate and inappropriate behavior. I wish you luck, I really do.