Deutsch and Englisch Schwestersprachen - German and English are Germanic Languages
 

My grandfather spoke German. In fact he got in trouble
for speaking German on the school playground. His
grandmother was from Austria. His grandfather was
from Germany. On my mother's side there are people
from Germany too. I have learned 5 languages but
not German which is part of my heritage. So how hard is
it to learn German and what is the relationship between
German and English?

German and English are both Germanic languages: that is, they
developed from a common parent language. English and German
are of course now separate languages but they still share 35%
common Germanic vocabulary and many similar grammatical
structures. In addition, over the centuries both German and of
course English borrowed many words from French and Latin, and
today German like Spanish borrows words and expressions from
English. Because of their similarities, German and English can be
considered sister languages. Learning German will be easier if you
look for similarities with English.

Guten Morgen. Kommen hier. Deutsch lernen.
Good morning. Come here. Learn German. (German learn.)

I can't tell how hard it is to learn German. Many complain about the grammar(articles, cases and some useless rules), though. I wouldn't necessarily say that English and German share many similarities, neither that their vocabulary have that much in common. I remember learning English vocabulary was a pain in the a**, couldn't find many words that are almost the same.
Though I'd say that most native German speakers don't have much trouble with some grammatical structures. It's definitely not Dutch, which you'd compare with Spanish and Portuguese.

I've known both English and Spanish native speakers who learned German and I wouldn't call it easy judging by their experience. It's definitely a stretch to call them sister languages. They have the same origin and a lot if the grammar and vocab will be somewhat familiar, unlike learning Arabic or Japanese or something completely different. Having said that, it's not a terribly difficult language either. The cases are probably the biggest stumbling block, but with only four I think it's manageable.

Gracias por tus comentarios.