Most languages in the world use Latin alphabet, even if they do not have any relationship with Latin. Known exceptions are: Arabic alphabet, Cyrilic one (for Russian, Bulgarian, etc), Japanese, Chinese, Hindi, etc, etc.
That means that all Germanic languages nowadays use Latin alphabet: German, Dutch, English, Frisian, Swedish, Danish, etc.
English is a Germanic language, as its origin is the emigration of German tribes (Angles, Jutes and Saxons) into what is now Great Britain. If you see texts in Anglo-Saxon, the primitive language, it looks much more modern German than modern English.
What happened later is that the Normands, who spoke a dialect of French, conquered the island and French was the official language of the country for centuries but only the upper classes used French, wheras the folk never abandoned English.
When English was made official again the language had been borrowed thousands of French words. As French comes from Latin, these are all in all Latin words.
Subsequently English took more words directly from Latin, usually words related to science, medicine, technology, philosophy, etc.
For more accurate information you can see this link, on the section "History"
http://en.wikipedia.org/wiki/English_language
That's why modern English is a Germanic language, with a grammar which is clearly Germanic but with more than 60% of its vocabulary which comes from Latin / French.
Regarding your last question: all Latin, Germanic, Slavic, Celtic, Iranian, Greek (among others) languages have a common ancestor, called Indo-European. This language is extinct and the most similar one is Sanskrit.
http://en.wikipedia.org/wiki/Indo-European_languages