It sounds like your children have been through a lot in a short period of time. They left their grandmother which had to have been very hard. My mother lives with us and I know how attached my children are to her. When we were having a new house built, she stayed with my sister while my husband and I were in an apartment with the children. It was only for a month but my children missed her dearly. Their behavior changed dramatically. My oldest, who loves school, suddenly refused to go on days when she knew my mother was coming.
Did your boyfriend live with you and the children before? If not, the children have to adjust to living with a different adult who probably has different rules and expectations of them. They are young and probably confused.
Have you tried having a special time with each of them to find out how they are feeling about all the changes. Your older two may find this helpful. If you give them a chance to tell you how they feel, they may be more inclined to listen to you explain how you feel when they are acting out. With regards to the chores I often remind my older daugther that when she helps me, I have more time for her. She gets it.
I borrowed an idea from Supernanny-the jewel jar. My children each have a jewel jar for chores and behavior. I have made chore lists, each chore is worth a certain amount of jewels depending on the time it takes to complete. They also earn jewels for getting "caught being good." Now, they lose jewels for specific behaviors. My oldest loses them for saying the word "stupid, stomping her feet and hitting herslf. My middle child loses them for yelling, hitting and not being a good listener. My youngest loses them for spitting, using "potty" words like poop and hitting. The appeal of the jewels is that they are worth money. Each jewel is worth ten cents. It doesn't sound like a lot but they are 8, 4 and 3 years old. They love getting the money because they can buy ice cream from the ice cream man or treats when we are out. They can also chose to save the jewels for a trip to the toy store or to have extra money when we go special places. My oldest is great at delaying gratification so she always saves her jewels.
Have you tried having some "mom" time? I have days when I can't wait for my husband to come home so that I can go and get milk. He always offers to pick it up on the way home but I have explained to him that even the half hour out helps. Sometimes I drive around for a while before going home and relax while he puts the kids to bed.
Please do not think I am trying to be a know-it-all. I certainly seek advice on the same issues with my kids. I have days when I am so tired and my head is pounding. I just wanted to offer suggestions and support so that you know that you are not alone.
Barbara