How are my 用词造句 ("use the word to make a sentence") sentences using 幸福 and 俩?
我妹妹十一月会结婚，太
  幸福了！
  
  他们俩今天在商店一起买新衣服了。


Basically, both of your sentences are ok grammatically. The first one can be improved if you replace 会 with 要. 


  我妹妹十一月要结婚，太幸福了！


要 sounds more emotional than 会 in this context. 会 is a bit "objective", less sentimental.  In this sentence, you want to express the excitement(indicated by 太幸福了！), so 要 is fit better. It's like saying, 我妹妹要结婚了！ 太幸福了！！！