[13] —sin intimidarle los gruñidos amenazadores, without being frightened by the threatening growls.
[14] —si te callas, if you can be still. ¿Pero dónde estará ese maldito perro? But where can that accursed dog be? Here estará is future of probability or conjecture. me las pagará, I'll get even with him (literally, he will pay me for them: las is an indefinite pronoun here and may mean las malas cosas, las ofensas, or something of the sort).
[15] —eran muchos y ventajosamente armados para vencerlos, were too many and too well armed (for him) to conquer them. In some expressions mucho means too much and muy means too.
[16] —matarían is conditional of probability or conjecture. Here translate Indudablemente le matarían, they undoubtedly killed him.
[17] —Si, why, or but.
[18] Que may be omitted in translating. Perhaps dices or some such expression was once understood before que.
[19] se te habrá caído, you must have dropped it.
[20] no se les da, is not given to them. Note that the subject of da follows the verb.
[21] —hacemos = haremos.
[22] —¿qué será de Juanito? what will become of Juanito?