You're likely right is not standard BrE. If it's standard AmE, then certainly in that case likely is an adverb and it is not a case of two adjectives put side by side.
If something is probable it has a good probability of happening, more probable than not. Possible
How to distinguish clearly the difference in meaning btw probability and posssibility?
(you know, I asked you the differenece btw "possible" and "probable", you have answered by giving "probability" and "possibility". So it's difficult for me to understand)
You can quantify probability: What's the probability that it will rain tomorrow? The answer may be very low, high, 70% etc. You can't quantify possibility; it either exists or doesn't exist. Is there any possibility of rain tomorrow? (however small)