How can I share my bitcoin wallet with my family members? Such that if my grandmother spends one btc one day, I see that reflected on my computer, etc.
This is also a great safety mechanism, in case one of our family member's hard drive crashes, the other members will still have the wallet.
If you're looking for something technically straight-forward, I suggest using an "e-wallet" and giving your partner access to the wallet account.
Review these links: https://en.bitcoin.it/wiki/Browser-based_wallet
And here are several e-wallet's listed: https://en.bitcoin.it/wiki/Category:EWallets
Electrum is a client that uses "deterministic keys", and thus multiple installations of the same wallet seed are supported.
(The only exception is if you import keys generated externally, an Electrum wallet those transactions are exclusive to the wallet in which they are imported.)
Also, Blockchain.info/wallet has a Desktop Sync feature which will keep your Bitcoin.org client's wallet.dat in sync with your Blockchain.info/wallet, and vice-versa. That doesn't mean you still don't need to backup your wallet.dat as it may not always sync perfectly but it does give a remote way for others to access your wallet.dat
