2) 은/는 is used when 2 or more things or people need to be compared, and when you want to emphasize something(or bring a topic). 이/가 is followed by the subject of a sentence. Here's an example conversation. A : 너희들 점심에 뭐 먹을래? What would you guys like to have for lunch? B : 나는 짜장면. I'd like 짜장면. C : 난 짬뽕. D : 난 볶음밥. E : 나도 짜장면. A : 그럼 누가 전화해서 주문할래? Then who will call the restaurant and order? E : 내가 주문할게. I will. Like in this conversation, if you want to talk about your own taste or choice compared to that of others', you use '은/는'. Here's another example. 인생은 짧고 예술은 길다 Life lasts short but art lasts long. (Compare art to life) 제인이가 노래는 잘 하는데, 그림은 정말 못 그려. Jane is a good singer, but a terrible painter. (Compare Jane's two opposite talents) 이 책은 동생이 빌려 온 거야. This book is borrowed by my brother. ('이 책' is a main topic of the conversation and 동생 is the subject of the sentence.)

1) 이십니다 is the most honorific form of 이다. For example, '저희 아버지는 선생님이십니다.' means my father is a teacher. What is 으십니다? Did you mean 있으십니다? 있으십니다 is another honorific form of 있다. 있다 has two different meanings. One means to exist and the other means to have or possess. The former one's honorific form is 계십니다, and the latter one's honorific form is 있으십니다. For example, 선생님은 지금 안 계십니다(means the teacher is not in now.), and 선생님께는 따님이 한 분 있으십니다(means The teacher has a daughter). It must be confusing, but I hope this will help you.