"Your son's nose is pointy and big."
This is a valid English translation, but not a good one. A good translation should evoke a feeling similar to the original sentence.
And the Chinese part is not too good either. I haven't seen many people talking about other's noses, not to say describing a nose with 又高又大. Besides, people usually say 鼻子尖 for "nose is pointy", rather than 高. 高 is for 鼻梁 (nose bridge).
you're right, 尖銳 or 尖 would be much more in keeping with "pointy". 高 would be more like high, as in set high in the face. at least, that's my understanding.
你的儿子的鼻子又高又大。 this is the literal translation for this sentence. To omit the first 的 makes more sense in a conversation, though.
Chinese use 高 when talking about someones' nose to mean pointy or that it sticks out. Surprisingly, this is a compliment!
No, using "高" to describe a person's nose (or rather the bridge of their nose) is often an insult.