Instead of the risk of having other people to have different part of your wallet backup the person should instead use another of his phone to import it so that they would have two phones that is controlling it.
I am reading a lot of bad advice in this thread. Using the same wallet in two different devices doesn't make you any safer, as a matter of fact it makes you more vulnerable to attack, because there are now two points of attack, and if any of them is compromised, the assets will be stolen.
I share my secret seeds with my brother even when it's against the rules. I still find trust in him, if you have a trusted ally you can as well share it with him in case of tomorrow.
There are no set-in-stone rules, you are your own bank, so you decide what to do with your seed phrase. If sharing it with a loved one is what works for you, then that is fine. There are also bitcoiners that share their seed phrase with their spouses, so it is what it is.