4. Only this shirt is a little less expensive than that shirt.
5. Elephants are much heavier than donkeys.
6.1. Our new house is a bit farther from the shops than old house. (не используется are)
6.2. The shops are a bit farther from our new house than [from] old house. (2 раза from, но последний в скобках можно наверно опустить, но по мне без него не очень)