Who owns the money in a Biscuit joint bank account?

You both own the money in a joint account equally. Either of you can use all of it, whoever paid it in. That's why it's best to open a joint account with someone you trust, and to agree together how you'll use it.

Can one person take all the money out of a Biscuit joint bank account?

Yes. Either account holder can withdraw or transfer the full balance without the other person's agreement.

We can't stop this from happening or reverse it, because the money in a joint account belongs to both of you. If you're worried about this, think carefully before opening a joint account, or only keep money in it that you're happy for both of you to use.

Who is responsible for what happens on a Biscuit joint bank account?

Both account holders are, including payments the other person makes.

Can we use a Biscuit joint bank account for business?

No, joint bank accounts are for personal use only.

What happens to the money if we split up?

Either of you can still use the account as long as it remains open, so it's a good idea to agree together what to do with the money. See What happens if we disagree or separate? for your options.