Good questions. Apostolic Succession to the Orthodox Church embodies 2 important facets: 1) laying on of hands tracing back to the Apostles and thus to Christ Himself and 2) continuation of the doctrines of the Apostles. When strays from either of these, the line of Apostolic Succession has been broken. The Orthodox Church feels very strongly that she has remained true in both of these areas. A careful examination of many doctrines (filioque, papal infalliblitly/supremecy, the new emerging marian dogmas, and many of the practices throughout the ages) shows that the RCC has strayed from the teachings and practices of the Apostles. When one is invalid, the Chalice too becomes invalid.
Now on to the 3rd question, and keep in mind this is my personal understanding and is not an offical statment from any of our patriarchs. In order for reunion to come, several things must change from the Roman end. The pope will have to renounce his infalliblitly/supremecy, vatican II will have to be recanted, the filioque removed, and some other issues I'm sure that I am not aware of. The Orthodox Church, since she believes so strongly she is the "Pillar and Foundation of the Truth" (1Tim. 3:15), will not bend on these issues. Things must always remain as they were in the early church.
~Maximos
