Transferring mothers funds to a joint account for bills

My mother may pass soon from hospital stay.

She has a will and stated to transfer all assets equally to her sons (myself and brother). She's an only child with no living parents. CA.

She chose not to name an executor though, and I am concerned that once she passes, no one will be covering her bills & mortgage. We can petition to be executors, but we would need her accounts' funds to pay off these bills - which I'm not sure will be available to us during probate.

I do have access to my mom's online banking accounts and my brother has a joint account with her. In case being executors doesn't help us, what if all her funds were consolidated in the joint acc? Her mortgage could also be prepaid for the probate process (WF doesn't have prepay penalties I believe). Not sure of the legal ramifications here, and I'm talking with an attorney.