In general, henches brought by anyone in the party contribute to the party’s success. However, you could do this instead, which would restrict the “GP Punishment” for extra henches to the PC who brought the henches, but wouldn’t get into math weirdness at 7+ henches.

Each PC has 1 share. If there are 4 PCs, each share is 25% of the hoard.

Each PC and henches have subshares; the PC has 20 subshares, the henches 3 subshares each. The share is divided by the total number of subshares, and split out appropriately.
For example, Alice (+3 henches), Bob (+1 hench), Catherine (+2 henches), and David (+8 henches) acquire a hoard worth 1,000,000 gold.
Alice splits 250,000 gold with her henches. The total subshares is 29, which means (rounded) 8,600 per share, so Alice gets 172,000 gold, and each hench gets 25,800 gold. The remaining 600 gold is put into the Team Alice Swear Jar for incidental expenses.
Bob splits 250,000 gold with his single hench (23 subshares): 10,869.5652173913 gold per share. Bob takes 217,391 gold and 3 silver, and his hench gets 32,608 gold, 6 silver, and 9 coppers. This leaves one copper over—Bob is an accountant in real life, so they track the subcopper portion separately to be awarded to the appropriate party upon earning a complete copper. Bob puts that copper in a special pouch.
Catherine splits 250,000 gold across 26 subshares: about 9,615.38 per share. She takes 192,307 gold and 6 silver, and rounds the copper in the henches’ favor: each hench gets 28,846 gold and 2 silver.
David splits 250,000 gold across a whopping 44 shares: about 5,681 gold per share. David gets 113,620 gold; each hench, 17,043 gold. The remaining 36 gold is put into a special fund Team David keeps for Wednesday Night Penny Gambling.