Some Workflow Foundation important and urgent doubts

Question

Hello,

 I have some doubts regarding Workflow foundation I hope someone can help me understand.

1. When we use persisting services using Sql, the workflow instance still remains running in memory?

2. Imagine I have a state-machine workflow, on my application I begin the workflow, sending parameters, letting it on a given state (let's call it state A). After, the instance stills running, and I want to someone else accesses that instance in order to aprove something and pass it into another state which leads to the end of the business process. 

2.1. How can I access a given instance id of a workflow from different applications, know which is its current state, and know that I only can perform a given action?

2.2. How do I guarantee concurrency access to a given instance of a workflow (ex.: 2 people accessing at the same time one instance)?

Hope you can help me figuring out!

Thank you a lot!