Hi, could someone explain to me what do the words in the parentheses next to the translations mean? Are they some sort of an alternative pronounciation?
There are 3 things that I don’t understand in particular:
いく = to go (に)
かえる = to return (destination に/へ)
And I’m not really sure what that symbol means “~”
Here’s a screenshot of the entire level, if someone’s interested: https://imgur.com/a/9S24Ddr
Regards.
I may be wrong as I am very new to learning Japanese myself.
But I believe the に and へ in the brackets are the particles that would go with those words in sentences.
Particles are in between other words in Japanese sentences to connect the words together to create sentences. Such as みせにいく (to go to the shop),
Oh and the ~ , the only time I usually see this in courses is when it is put before counters in Japanese, such as ~かい which is used as にかい (second floor).
I am probably completely wrong with it all though, lol. But thought I’d have a crack at trying to help. 
~をのむ
The ~ can be anything. さけ をのむ, みず をのむ. It’s just to tell you that the object comes before the verb.