Translation:The siblings are walking along the way.
Why accusative ("den") ?
Edit: OK I think I got it: entlanglaufen is a transitive verb according to (1) so it will be accusative according to (2).
That also answer why the word “entlang” is at the end of the sentence. Thanks.
In pronunciation, is it correct to say the g in Weg sounds like k, while the g in entlang does not?
Yes, the first one does sound like a "k" (it must to, indeed), I'm not completely sure, but I think It is because there is a vowel before.
Are the prepositions near the end in German? Because I think I see a trend here....
Entlanglaufen is a single word, a trennbar (separable) verb. Whenever you have a separable verb, the separated preposition goes to the end of the sentence. Other examples include mitbringen, mitnehmen, aufpassen, etc.
Because it is a single verb “entlanglaufen”, and the “entlang” is a separable prefix that is placed at the end of the sentence. See njm37’s answer and spawarotti’s post with links.
Why is "the brother and sister" not accepted when one of the offered translations of Geschwister is "brothers and sisters"? Any combination of two or more should be accepted; one brother and one sister are still siblings plural.