The ladies on the board have done a wonderful job of pointing you in the right direction!
If you are wanting to combine your kiddos, I would put both of them in "Little Hearts..." for the left side of the plans each day (and the storytime box from the right side of the plans). I would teach all of "Little Hearts..." to your younger one.
For language arts for your older one, I would get the "Beyond..." guide and follow the emerging reader schedule in the Appendix and follow the spelling plans and the gentle grammar lessons each week in the "Beyond...." guide as well.
By the time you spend the money to purchase "A Reason for Spelling" and "Growing with Grammar" you could have purchased the "Beyond..." guide and already have all of those areas included with a reading schedule too (and have your "Beyond..." guide for the following year too).
A Reason for Spelling does have instances where kiddos must find the incorrectly spelled word (which reinforces the wrong spelling). Growing with Grammar is pretty intensive for the early years, and while kiddos are still gaining as readers and writers it is better to wait with intensive grammar instruction another year.
Having said that, you know what fits your family best, and are welcome to do what you choose to make our programs fit you and your style!
Blessings,
Carrie