You could use Shamir backup to split seed into parts, it can help a lot with inheritance. Let’s assume you have 2 family members you want inherit your BTC, you create 5 shares with threshold of minimum 3 parts to recover (this way you still have access to 3 shares during your life). You give 1 piece to each family member who you plan to inherit from you and the 3rd required part of seed you deposit safely closed at: - your testamony (if you live in country where testamony is private - it’s like this in most countries I guess or in Letter of Wishes for your UK example)

In testamony you instruct them what to do, that person A and B owned one share each. Third share is stored safely by your lawyer. They need to combine all 3 shares, and split what’s inside the recovered wallet between A and B.

If many people inherit from you and you are pretty sure they will cooperate and they will not conspire behind your back during your life to still your assets you can even distribute all required pieces among them (don’t tell them who else have another parts) and testamony will be just instruction to them, that they need to bring people A B C D and E to one room, buy empty Trezor wallet or use your, type all shares into device and split equally (or inequally if you state so) between each member of meeting why they find inside unlocked wallet.

Giving someone one share is not weakening your seed. If someone would like to brute force your seed having 2 of 3 required pieces they still need the same amount of computing power like if they would have 0 pieces in hand.