A friend who had recently had a baby, was invited to family mediation with her partner, his ex and their 2 teenage children who were very unruly at the time and hated their dad's new partner.
My friend, the new partner, said the sessions were awful for her (very emotional and shouty) and it emerged that the teenagers were jealous and wanted to spend more time with their dad. He was out at work all day so she, the stepmother, had 2 sullen teenagers and a baby to look after! She was not impressed.
The couple are no longer together and he married someone else and fathered more children!
Meanwhile, my friend branched out on her own taking their DC with her. DC is now an adult and all seems well .
I hope you know what you're letting yourself in for!