So, are each of these books seen as having equal authority and reliability?
Yes, but there is a however. The KJ Bible is held to be the most correct Bible available but it is still believed that important pieces were translated incorrectly and/or omitted. Very little scripture (compared to the total Bible) falls into that category, however. All four books stand together as a testimony of Jesus Christ and his true gospel. Each book is equal in authority and reliability.
Are these talks considered equal to each of the books described above, of greater authority, lesser authority?
In many respects they are more important because they are the current counsel given to the members that specifically meet the needs at that time. Let me use an example to illustrate. Back in Brigham Young's days he was responsible for moving the saints to the West. There was a great deal of counsel given at the time to facilitate this endeavor. It was of great importance that the saints follow the counsel exactly as given. Today, however, we are not engaged in such an endeavor and much of the counsel given at that time would be out of place today.
Another example would be counsel given just a few months ago. Elder Holland of the 12 Apostles gave counsel regarding Sunday, Church attire, "Our clothing or footwear need never be expensive, indeed should not be expensive, but neither should it appear that we are on our way to the beach." This was reflective of the onslaught of flip flops that has made it's way into youth attire. This counsel is only valid today. Members 100 years ago wouldn't have been caught dead in something like flip flops, especially at Church!
Gospel truths, however, span eternity. A talk given by Brigham Young on the atonement would still hold true today, in fact might be referenced by the current Prophet. Those talks and any current counsel are held in equal value with the four books mentioned previously. With the caveat that current counsel may only be applicable to the current time frame. Whereas the scriptures (the four books) always hold as scriputure.