PAST AND PRESENT
X I've been in London yesterday.
To talk about a particular time in the past, use past simplel.
V I was in London yesterday.

! How long are you in Cambridge? - Since May.
If you say How are you in Cambridge? you are talking about time that includes the future, e.g. until May. For time including the past and present, use present perfect.
V How long have you been in Cambridge?-- Since May.

CHARACTER
X I have good relations with my father.
In politics, contries can have good relations with each other. With family and friends you have a good/bad relationship.
V I have a good relationship with my father.

X I've never met your sister -- how is sh?
You only ask How is she? If you know her. The answer might be She's fine/very well. To ask about the character of someone you don't know, ask:
... What's she like?

X I enjoyed meeting your brother at the party - he's very sympathetic.
A sympathetic person understands your problems and feel sorry for you. A person who is easy to like, is very nice and likeable.
V ... he's very nice.