How do you calculate returns per individual investor and value of fund?

If you create a fund through a LLP or S-Corporation, how do you calculate returns per individual investor and value of fund? For example: 5 people each invest $2000 each on January 1st. Each individual investor cannot take out initial investment until 6 months after deposit. September 1st, value of fund = $11,000. Investor A wants to take out total initial investment plus gains. How do you maintain the value of the fund with that loss?How do you calculate returns per individual investor and value of fund?
lets say shares cost $1000 each, meaning the NAV (net asset value) of each share is $1000





so when each investor paid $2000 they each got 2 shares.





On september 1st the value of the fund is $11,000 or $1,100 per share. Investor A takes out his money, he sells his shares to someone else for $1,100 per share or perhaps somehow he can just take out his $2,200. Then what would remain is a fund worth $9,800, with 8 shares, each worth $1,100.