신 is to make it formal. To show respect for the person you are talking about. For example, 우리 할머니 괜찮으신데... (Our grandmother is fine but...) So let's say you're talking about your little brother, then you don't need to use the formal language, right? So you'll take out 신 and instead say 내 동생 괜찮은데... (My brother is okay but...) 데 is to connect the part before the words with 으신데 to the part after. And it usually means "but". So you use it when you wanna say something that's contrary to what's already been said. For example, 우리 할머니 괜찮으신데 아직 쫌 쉬셔야 돼 (Our grandmother is fine but she still needs to take some rest). Hope it helps! :)

Inflectional suffixEdit -ㄴ데 (-nde) 1. mentions relevant circumstances before explaining, commanding, or suggesting 밖이 시끄러운데 무슨 일 있나? The outside is noisy; maybe something happened? 날이 좋은데 어디 놀러 안 갈 What a good weather! Why don't we go somewhere to have some fun? 2. an intimate style exclamatory or interrogative suffix, expressing unexpectedness or anticipating the listener's responses 그렇지만 나이도 있으신데... But he is aged, so (doing it is dangerous)... 여, 제법인데? Oh, nice performance; better than I expected! * Usage notesEdit The suffix -ㄴ데 (-nde) takes the sequential form of an adjective or 이다 (ida, “to be”), and if the adjective ends in ㄹ (l), the ㄹ (l) drops out. For verbs and existential adjectives 있다 (itda, “to exist”), 없다 (eopda, “not to exist”), and 계시다 (gyesida, “to exist (honorific)”), or to make use of non-present tense, -는데 (-neunde) is used. Not to be confused with -ㄴ 데 (-ㄴ de, “-n de”), meaning the place where the event -ㄴ (-n) indicates happened, or the event itself. See 데 (de). * Add -시- to make the formal polite style expression.