Being P1, I don't worry much about this scenario. At least in my perspective, I have people that I can trust very much, and the problem is finding someone I can trust that won't be giving the funds as ransom to save me from danger.
There aren't many people I'd truely trust with a large amount of money. I mean, how well can you really know someone? Finding someone who wouldn't save you is the easy part

One possibility might be to have a 4-out-of-6 multisig with P1 and P2 holding 2 keys each, and P3 and P4 holding 1 key each. What do you think of this idea? No four keys are in a single continent, and we can know for sure who signed a transaction.
That makes it less likely for P3 or P4 to strike a deal, but makes it more risky to recover the funds when needed. Say P1 dies. Now P2 needs both P3 and P4, while P3 only trusts P1.
I'm afraid we may let you down with our privacy commitments, though. While ideologically we are totally in favor of private transactions, for several reasons we don't want people to use our exchange to mix bitcoins. We may actually do the very opposite and publish all transaction data allowing anyone to link withdraw and deposit transactions
That would be very, very bad! I've never seen any website that publishes all transaction data, and within EU it could even be a GDPR violation.
I assume any exchange keeps trade and transaction data forever, and if they ever need to provide it, they can dig it up.
TL;DR: don't do it. You'll scare away your customers.
By doing so we can counter the argument used by governments that exchanges either have to require KYC identification from all users or else they are complicit in money laundering.
I don't think any government would accept your "counter argument". If you fall under a certain government's jurisdiction, they can already demand you hand over transaction data. And any government that doesn't have jurisdiction shouldn't necessarily trust any data you provide.
in some sense your account is just like a set of public addresses in the blockchain.
It will be a centrally controlled database, meaning you can put anything you want in there, so anyone accused of anything could just deny it and government won't have conclusive evidence. Or you could be bribed to change something.
The "Entry Price" tells you what is the reference price. So if you have a long position, you need to sell higher than this price to make a profit, and if you have a short position, you need to buy back lower than this price to make a profit. If price moves against and reaches the "Liquidation Price" you may get liquidated and lose the amount frozen.

Do you this explanation helps? Please let me know whether there is anything else that is still confusing to you, as anything confusing you is likely to confuse to many other people too!
I wanted to test it, but I now get this:
Login Error: We cannot find a valid account with this credentials