Private company has 30 shareholders. Company is considering making a stock offering to raise capital.

One stock split happened a number of years ago, 3 for 1.

Currently, there have been new investors with cost basis of stock much higher than what president is considering for new offering ($100 newest cost basis against proposed $20 stock offering).

How should a stock split be calculated in such a situation? take the highest cost basis split that to equalize to the newest offering, to protect the ratios?

So in the above example, 5 for 1?

Thank You.