We live 3 hours south of
SS.
BM has alienated SS from our family for years. SS is 7 years older than DS1 and DS2 (ages 9 and 8 respectively.)
For years BM has told SS that DS1 and DS2 (as well as
DH and I) were not his REAL family. He was bribed every time he got disciplined here for harming his little brothers or tormenting them.
A year ago, SS was convicted of Child rape in the first degree. He victimized my two little boys for almost 2 years before we discovered it. His excuse for why it was not wrong? "They aren't real anyway."
We are the worst case scenario. We have kicked ourselves many times for not seeing this coming. We blame ourselves for not MAKING SS continue in counseling. The lack of $$ and the distance was not really an insurmountable obstacle. We thought so at the time, but if we had another chance we would find a way to make it work, even on an EOW schedule and with significant interference from BM.
At age 9 SS was showing significant angst for DS1 and DS2. He has threatened to call
CPS when he was punished for taking a stick and beating DS1 with it. We have had to enforce a strict "my house my rules" position with SS for years. We also warned SS that if he ever called CPS and alleged abuse, they WOULD find some when they showed up. The fear of it was enough for a while.
Do whatever it takes to get family counseling. Buy and carry a tape recorder and catch SS saying these things. It might be enough to get counseling COURT ordered. Start looking for a counselor now. Take the boys if you can get an appointment.
Don't let this escalate. Your baby may be at risk. DS1 has been choked, stabbed, beaten and raped before the age of 8. DS2 has been punched in the head, struck in the back/spine, attempted smothered in his sleep, and raped, all before the age of 6. We should have seen it, but the kids didn't tell. And as you have found, all that yelling seems normal for siblings interacting.
Now SS has zero contact with DS1 and DS2. He spends no time with any of his cousins. He is still on probation with jail time hanging over his head if he does not complete sex offender treatment. DH has his parenting time separate from the younger kids. That may be necessary in your case for the safety of the baby.