If you're uneasy giving the seed directly to your heirs, one suggestion would be to scramble the seed given to them by assigning each word an arbitrary number. In the private letter given to the executor you can provide the correct seed phrase order using the arbitrary numbers along with the passphrase.

Agree. Giving seed to heirs, as well as successor heirs creates at least some redundancy.

Leveling up to multisig is better. This is plan you can set up today, at almost no cost. So you’re not walking around with no plan at all.