OK, let me clarify a few things!
The lock I had put on was just an internal bedroom door, not the external doors.
I need to check what she said as well about having the right to change the external locks - I asked her even if we are joint owners and she said yes. What the repercussions of that might be I have no idea though.
He has never had possession of my phone. He has just given me a new replacement sim as there was something wrong with the old one, and I still have the old one. He has never touched the handset. He is not techy anyway, has a different phone from me, so wouldn't expect him to know much about this.
We are joint owners, 50/50.
I've not specifically addressed the house sale issue. I am clinging on to the hope that if I go to court, under the Children's Act, a property adjustment could be made (awarding me 70% and him 30% for example), a lump sum awarded, or much higher child maintenance than the minimum via the CMS. Any of these options would enable me to eventually afford to buy a property on my own in the same area (once I'm working and could get a mortgage on my own with a large deposit).