What can't you do when you have lasting power of attorney jointly and severally for property and finance?

Well, for one thing, you cannot make medical decisions. That would be covered under a health care proxy. Much depends on what was in the power of attorney document. I suggest you contact your county office of the aging to see if they can help.

I think what you are saying is that the principal, the person who has created the financial POA, named at least two co-agents and now the principal is no longer competent to make their own financial decisions. If the POA names more than one agent, look at the document itself to see if the principal included instructions on how disputes between or among co-agents should be worked out. For example, the POA may say that co-agents can make decisions independently of one another, which seems like a bad idea. Or the POA can require that the co-agents agree. If there are more than two co-agents, the POA might say that the majority rules. If the POA does not clearly spell out how to resolve co-agent disputes, consider mediation. Or check with an attorney to see if your state has a statute that addresses resolving co-agent disputes. You can also ask the court to decide. As for what any POA agent can't do is to fail to act in the principal's best interests. Following the Prudent Investor rule can be complicated, so consult a trust and estate attorney if you have questions.

Did you mean durable power of attorney?

We don't know what it says. So that is the only way to know for sure what can be done with it.

Read it, if you do not understand it, ask an attorney.

from Google search

Joint and Several Attorneys

If Jane's power of attorney for property gives Mark and James the authority to act jointly and severally, this means that they can each make separate decisions without the other person's agreement or sign-off on same.