Fractional share positions will operate just like whole shares. All fractional positions of AAPL will receive 4x the amount of their pre-split position and all fractional positions of TSLA will receive 5x the amount of their pre-split position.
For instance, if you owned 0.5 fractional shares of AAPL, you would receive 2 whole shares post-split (4 x 0.5) in exchange. If you owned 0.5 fractional shares of TSLA, you would receive 2.5 shares post-split (5 x 0.5) in exchange.
To learn more about stock splits and why they happen, read more https://www.sofi.com/learn/content/what-is-a-stock-split/.