Short answer

If a family member uses your computer occasionally, the wallet on it is at non-trivial risk — even with the best intentions, accidents happen (clicking phishing links, installing browser extensions, leaving the screen unlocked). The mitigation depends on stakes: for under $5K, your wallet password is probably sufficient. For meaningful holdings, the wallet should live on a separate device that family members don't use, or behind a hardware wallet that requires physical button-press for transactions.

The realistic threats from family use

Not "your spouse will steal your crypto" — usually that's not the issue. The actual threats are:

Phishing exposure. Your teenager clicks a "Free Robux" link, installs a browser extension, and now the same computer's wallet extension has neighbor malware. The extension can capture your seed phrase when you enter it.

Accidental approval. A family member opens your unlocked computer, sees the wallet app, clicks a popup, doesn't read it, hits "Approve." If your wallet extension was open, they may sign a transaction or grant approval.

Saved password access. Your computer's password manager has your exchange password autofilled. A family member with computer access has logged-in exchange access.

Cookie hijacking. Your browser stays logged in to Coinbase. A family member opens the browser to "check email" and the Coinbase tab is right there.

Defense by tier

Tier 1 (low stakes, under $5K). Strong wallet-app password. Auto-lock the wallet after 5 minutes of inactivity. Don't save the wallet password in the browser. Lock the computer when leaving the room.

Tier 2 (medium stakes, $5K-50K). Hardware wallet — Ledger or Trezor — that requires button-press for any transaction. The wallet app can be installed, but no transaction goes through without physical confirmation. Family use of the computer becomes a non-issue for crypto specifically.

Tier 3 (high stakes, $50K+). Dedicated computer for crypto. Old laptop, fresh OS install, no other software except wallet apps. Family doesn't use it. Crypto activity happens only there. Combined with hardware wallet for actual signing.

The shared-computer hardware-wallet workflow

Even on a shared computer, a hardware wallet provides strong protection. The shared computer can have malware, the family can poke around — but every transaction requires the hardware wallet to be plugged in, unlocked with PIN, and confirmed on its on-device screen. The attacker (or accidental family member) sees a popup but can't physically press the hardware-wallet button.

The exception is if the family member sees your hardware-wallet PIN. Don't enter the PIN with someone watching. Don't write the PIN on a sticker on the device.

The talking-to-family piece

For US households where one person manages crypto: have one conversation with the family about what's on the computer and why they shouldn't click anything that pops up. Most spouses and kids will respect this; the goal is to prevent accidents, not to suspect bad intent.

For estate-planning purposes, the family should know the crypto exists and how to access it if you're incapacitated. But that's a separate conversation from "don't click weird popups today."

Further reading: Hardware wallet, Hot wallet.