Your honesty will be a virtue when speaking in court, so don't regret it. Remember judges are used to being lied to, but they won't be manipulated and take a stance against anyone who tries to lie or cover up as with your sister.
Sometimes we need to be careful what we put on the web, because as others have said, it is open to everyone to read. You haven't given away any names though.
Having asked for the venue to be changed with no luck, I guess that is something you will just have to accept.
I am sorry that the solicitors didn't phone back, in my experience they can be very slow in doing so. They called me back on the night before the hearing!
In the COP, I would imagine that many people represent themselves for financial reasons, and, as I have said previously, the judge isn't hard on "non-legal" people (he expects legal people to know the rules
). He will ask questions and listen to representations from both parties; be calm, truthful and never interrupt even of you hear your sister telling untruths, you will have your chance to speak.
Take a notepad with you to make notes of on anything that you want to question, probably from your sister's words!
As Grannie G has suggested, I found the Alzheimers helpline very knowledgeable and helpful. They gave me certain phrases to use too, which helped a lot. e.g. respecting human rights.
I think that, although you will be nervous on the day, you will surprise yourself as to how strong you can be when your mum's safety and welfare is at risk.
J x