ETF companies are primarily for-profit companies so they will most likely choose the network that they believe will give them the greatest profits in the event of a hard fork.
As big capital management companies, they will think of safety for capital they are managed, not profit first. Because profit can be gained later when chaos ends and risk is smaller, they can find new opportunities to get profit. If they lose capital of their customers, they will go bankrupted and go into jails.
ETF companies don't own private keys and they will have to depend on their partners, the custodians like Coinbase, to claim forked coins. If Coinbase support, I believe they will do, fork claims, ETF companies will not lose anything.
The 2017 hard fork create Bitcoin and Bitcoin Cash, but we see the main chain, Bitcoin continues to grow, higher and higher in hash rate and price. Bitcoin Cash, the forked coin is like a bonus.
This means that they will most likely choose the network in which the price is higher or the number of investors is greater. As for ETF investors, they do not have the right to object or choose the network that suits them because in reality they do not own Bitcoin, but rather own shares in these companies, and therefore they are forced to accept the choice of networks that the companies choose.
ETF investors depend on ETF companies which in turn depend on their third-party partners, custodians for example Coinbase. It is like chain of risk from customers to ETF companies to Custodian service providers.
