But each family member will have their own seed phrase. When generating a new seed phrase, of course, you can create millions of BTC-wallets, but this creates a problem due to the increase in the number of seed phrases (all this needs to be saved).

The point is to be able to create the maximum number of addresses with one seed phrase.

Of course, there are different types of btc that can be used, which will increase the limit of available addresses. But, for example, in signature campaigns, the segwit type is used and with frequent changes of campaigns, for example, this limit will be quickly exhausted.

If we also take into account the undesirability of reusing the same address, then the limit in BTC-addresses will still be quickly exhausted.

These are theoretical figures, in practice, it will be less. At least because, for example, old types of addresses (legacy) are used less often, which means you will not be able to use it.

I'm not sure about the tons of wallets, but there is 1 way to increase the limit that I found. This is the presence of a standard and hidden wallet, which allows you to increase the number of wallets by 2 times. You can switch between this types.