This is certainly an aggravation, isn't it? The best laid plans can be derailed good and proper by siblings bickering and fighting. The families that I have spoken to have shared that teaching siblings to be kind to one another is certainly a priority in their homeschools.
Having five boys myself who are very close in age I can relate on a personal level with this issue. All five of my boys shared a bedroom when they were young. I can tell you that sometimes that bedroom was more like a battleground than a place to sleep. :)
I sense that you know that the problem is one of maturity and instruction. Stay on top of the issue and do not let unkind behavior slide by. It is very important that we teach our children how to treat one another. Surely this is a priority in our religious instruction in the homeschool.
Talk out the issues when it seems that the arguments are more serious than usual. Let each of the parties involved have a say. Make certain that everyone understands that being unkind and saying hurtful things is not only unholy but it is hurtful in a way that is deeper. I would tell my boys that they are each other's best friends. Furthermore they were blest to have one another and would find one day that they mean so much to each other.
Serious arguments require serious intervention. Silly prattle needs only sending everyone outside to play off the steam. My best discipline method was to give everyone a dust cloth and have them dust the baseboards as 'thinking time' when they were hateful to one another. Sometimes I would give the offenders a task that all had to do together, like weeding the garden.
Recently the boys were sharing about their growing up. They all agreed that when I sent them to weed the garden I became the focus of their conversations while they worked and there developed a kinship between them. I think that what they were trying to tell me is that being punished together was clever in that they soon forgot the argument and chose to focus instead upon the unfairness of life and moms who make you weed the garden. :)
When you pray the rosary in the evening, have the boys offer up the decades for one another. This is something that we have done for many years and I truly believe it makes a difference. When the children pray for one another it is powerful. Prayer changes hearts because it has the power to do so.
Hang in there, mom. Bickering has the potential to steal your peace and make for a tiring day. Bless your heart, I know where you are coming from. Ask the Lord to shower you with grace and temperance in your discipline. It is vital that our behavior when we discipline imitates the good and sweet Jesus. This is difficult at times. We are in need of the Lord's abundant graces. I have gone to confession many a time with the words, "I have lost my patience with the children." One time when I had had a particularly troubling week full of frustrations with this issue, I went to confession with an elderly priest. As he prepared to say the beautiful prayers of absolution he looked me in the eyes and said, 'You know how very much Jesus loves you. He forgives you your sins and wants to help you deal with all that surrounds you. Call upon this strength and rest in the power of His love.'
My little boys are not so little anymore. I would like to 'shrink' everyone now and then back to the days when the biggest issue was who took whose he-man toy. :) They are close to one another and speak with one another at least weekly if not more. If I want to know what one is doing or where they are going I only need to call one of them. They are indeed each other's best friends. Praise God. I thank the Lord for this gift nightly.
Let us pray together a Hail Mary for your intentions. I will pray today just for you and your boys.
Lord, I praise You and thank You that in Your mercy You have allowed me the great gift of seeing the joy that is beyond the frustrations. You have allowed me to be a mother though I know I lacked all that was necessary to do this well. Your teaching is gentle and kind. Amen.
Sending out a prayer,