Cum pompa ad templum appropinquaret, tibicen eos qui cantabant lente sequebatur.

The imperfect is used for actions that were ongoing, in progress, or descriptive in the past. The sentence is painting a scene:

• the procession was approaching
• some people were singing
• the flute-player was following

So the imperfect fits the idea of continuing past action rather than a single completed event.

Ad templum means toward the temple or up to the temple. It shows the direction of movement.

A useful note: many learners also meet appropinquare with the dative, as in templo appropinquare. So this verb can be seen with more than one construction in Latin texts and teaching materials.

Because Latin often uses a demonstrative + relative clause together:

• eos = those / them
• qui cantabant = who were singing

Together, eos qui cantabant means those who were singing. This is a very common Latin pattern.

Because the two words do different jobs.

• eos is accusative because it is the object of sequebatur
• qui is nominative because it is the subject of cantabant

A relative pronoun takes its gender and number from its antecedent, but its case from its role inside its own clause. So qui refers back to eos, but inside qui cantabant it is the one doing the singing, so it must be nominative.

Most naturally, lente modifies sequebatur. So the sense is that the flute-player was following slowly.

Because Latin word order is flexible, an adverb can sometimes leave room for ambiguity. But in this sentence, lente sequebatur is the most straightforward reading.

Yes, but it is not rigidly fixed the way English word order is.

• Cum pompa ad templum appropinquaret comes first to set the scene
• tibicen appears early in the main clause to identify the main subject
• eos qui cantabant stays together as a unit, since qui cantabant describes eos
• lente is placed near sequebatur to show the manner of following

So the order is natural Latin: first the background, then the main action, with descriptive elements grouped clearly.