Biting/Hiting Stage HELP!!

I had another baby 5 weeks ago and ever since my daughter has started hitting/biting randomly. Mostly myself and my partner but at times the baby too as much as we are trying to protect him. We tell her off and if both of us are here we had been putting her in her room (hard to do if I’m alone and BF at the time) but she has good understanding and vocabulary for her age and says she will behave, won’t hit again and says sorry but then can do it numerous times again that day. We have been making a conscious effort to do things with just her/take her out to the park just herself etc. Is anyone else experiencing this/does anyone have any tips of how to stop this/any tips especially for when I’m home alone with the 2 of them. Thanks