I had this issue with my sows. I have a bonded pair of sows about 2.5 years old and adopted a 4 week old baby from the shelter where I work. I did introductions properly, gave them 5 hours and then put them in their new cage (2x5) and everything went downhill. My dominant older sow was fine with the baby, a few nips during floortime but that was it but my less dominant sow went insane after they were put in the cage. She was intense chasing and squealing and nipping at the baby. Wouldn't let the baby eat, even though there were 3 of everything around she was even more determined to get the baby rather than her own veggies. Then my adult sows started fighting. Tons of teeth chattering and nipping which I never see from them. I ended up separating because the baby got a wound on her shoulder (not terrible but missing hair and small bleeding teeth marks) and my one sow had a huge chunk of fur missing from her face, no blood but it definitely would of escalated to that.
I ended up getting another baby pig from kijiji, introduced them and they love each other and as soon as I put my adults back in their 2×4 with their original hideys they were back to 100% normal like they used to be. This all happened About 6 weeks ago and I made the right decision for sure. It was way more than dominance behaviour and now both pairs are living very happily with one another!