The first word you circled, "slowly", is correct. It is an adverb that modifies the verb "walked". It describes how they walked.
The second word "beautifully" is not an adverb. It's an adjective. It modifies the noun "buildings". It describes the buildings.
The third word you circled isn't correct either. "Paintings" is a noun since it's an object.
The word "moved" is a verb, so that isn't an adverb. However, "quietly" is an adverb since it describes how they moved. An adverb modifies or describes how a verb is performed.
The fifth word you circled "playing" is not an adverb. Instead, "beautifully" is an adverb. As a fairly general rule, if you see "ly" at the end of an adjective, then it becomes an adverb. The word "beautiful" is an adjective while "beautifully" is an adverb. The adverb "beautifully" describes how the violinist was playing, with the very "playing" being the verb.
The word "loudly" is an adverb. It describes how the trumpet player is playing.
The summary of all this is shown in the attachment below.