I don't know how you can prove absolutely that Jane and Ann are siblings of Abel and Sarah unless there is a clue at the records office; such as same occupation for William Hosier. I think, based on the information to hand (IGI records), that it is very probable that they are.
William and Jane were married in 1744. It was very common to name children after the parents or Grandparents so Jane christened in 1746 is not a surprise. Ann christened only 4 months later is, but I guess Jane was born sometime well before she was christened. Sarah was christened in 1750 and Abel in 1753. As I stated in my earlier email Kings Langley is very close to Hemel Hempstead. A visit to the records office in Hertford may be your next step if it is not too far..