Ex baby mum drama!!

So but if a long one..

Recently me and my long term partner broke up. He has a child of 5years old from a previous relationship who stayed with us every weekend.

My ex’s sister has text his baby’s mum and said there is lots of tension in our house atm (we are staying living together until the end of the month when I will get a flat) and that we are arguing all the time. This is not true at all, and in fact we are been very civil, even watching tv together on an evening etc.

Now for whatever reason, his sister said this. Not his baby’s mum is refusing to let him come to the house because she doesn’t want him around the tension.

My ex has explained that it is not true at all and that he would never involve his son if that was the case. She is now claiming that the breakup between me and him is going to confuse their son and she doesn’t want him involved( we were together for 6 nearly 7 years)

Does she have any rights to stop him seeing his son because of hearsay/gossip?