Interest equalization in a fund, how to calculate.

I am dealing with a calculation of the interest equalisations to be paid in a hypothetical investment fund. The situation is as follows (with simplified terms):

The first group of investors (investors 1 and 2) join the fund on 1.1.2020, with both committing $100 ($200 in total) into the fund. On 1.10.2020 the fund calls $40 in total from the investors (call 1), on 6.6.2020 the fund makes another call of $60. A second group of investors (investors 3 and 4) join the fund on 1.1.2021, with both committing $50. On 6.6.2021 there is a capital call of $50. On 1.1.2022 a third and final group of investors (investors 5 and 6) join, both committing $60. The investors participating in subsequent closings are required to pay interest at a rate of 5% per annum to existing investors, calculated on previously called capital, as compensation for earlier entry.

How should the equalisation between investors be calculated? Specifically the issue I am having is trying to figure out, how does the third group of investors compensate the second group regarding capital calls 1 and 2. Should the second group be compensated by the third group for the capital they contributed upon joining the fund, or only for the calls that were made after the second group had already joined?