Short answer
Technically possible, but extremely not recommended. A mnemonic equals full asset control; sharing means any one person can unilaterally drain everything. Even in marriage, parent-child, or business-partner relationships, people change and relationships can break. The correct approach is Shamir secret sharing (split the mnemonic into N shares, M required to recover), multisig wallets, social recovery wallets, or a formal trust through a law firm.
Why mnemonics are not bank accounts
Banks have rules, customer service, and law. The blockchain has one rule: "if you can produce a valid signature, you are the owner." A mnemonic in three people's hands means three identical house keys — any one can clean the house out, and after the fact there's no telling which key was used.
Business partnership scenarios produce this failure repeatedly. When the project is going well, everyone is a brother. When there's a problem — technical disagreement, funding fall-through, someone urgently needs cash — one partner moves the funds overnight. In crypto, a lawyer's letter lands on cotton.
The coercion risk
Three people each holding the full mnemonic equals three independent attack surfaces. An attacker need only find the most socially vulnerable family member. "Sharing" multiplies risk by N rather than dividing it.
The four correct approaches
Shamir Secret Sharing (SLIP-39). Built into Trezor Safe and OneKey Pro. Split the seed into N shares with M-of-N threshold. Example: 2-of-3 — give one share to spouse, one to a sibling, one in a bank safe-deposit box. Any two reconstruct; one alone reveals nothing.
Multisig wallet. Three independent keys, two required to sign. Used by exchanges, DAOs, high-net-worth individuals. Safe (formerly Gnosis Safe) on Ethereum, native Bitcoin multisig via Sparrow Wallet.
Social recovery wallet. Argent Wallet's model — primary key for daily use, "guardians" can collectively rotate the key if lost.
Formal estate planning. US residents can have a crypto-aware estate attorney draft a will with sealed-envelope instructions for executors. Casa and Unchained Capital offer managed services.
Further reading: Shamir Backup, Multisig.