Meaning from Merriam-Webster -
As for -
(meaning) with regard to/concerning.
He's here. As for the others, they'll arrive later. [=the others will arrive later]
He was a nice enough person, but as for his suggestions, I found them unhelpful.
As to -
(1. meaning) about.
I'm at a loss as to how to explain the error. [=I don't know how to explain the error]
There is disagreement as to the causes of the fire.
I remained uncertain as to the value of his suggestions.
(2. meaning) according to, by.
The eggs are graded as to size and color.
As you have learned about the individual meanings of as to and as for, it's advisable to please go through the following usage notes. Because in some places they almost mean the same, so which one to use over the other.
Notes from Modern English Usage -
Some older uses of as to meaning 'with respect to, with reference to' (e.g. As to myself, I'm not satisfied - D. Hartley, 1748) have given way to as for (e.g. As for you, son, your mother will hear of this). As to survives, however, when the noun governed is non-personal (e.g. As to the matter raised at the governing body, my view is ...), and especially when the sense required is 'according to, proportionate to' (e.g. correct as to colour and shape; the rates of postage vary both as to distance and weight).
As to is frequently used with subordinate questions, as in The Politics Fellow left no instructions as to whether you should write a second examination paper or not. It's also used after certain preceding passive clauses (e.g. I am not much troubled as to its outward appearance - G. Gissing, 1903). In most circumstances, though, as to is best left unused, especially when other constructions are available or when its presence is simply unnecessary: He asked his mother (as to) when he would be regarded as old enough to go to discos. He reminded me how to behave is a better construction than He reminded me as to how I should behave.
As for sometimes implies a degree of scorn, e.g. As for Smith minor, he can't even swim across the baths yet, or a threat e.g. As for you, son, your mother will hear of this. But not necessarily: As for me, I was more than content with the description of me as a map of low desires - H. Jacobson, 1986.
If you go thorough all that was written above I can expect you have a clear understanding of the meaning of that two phrase and of when to use the one over the other. From that knowledge you can now yourself tell which sentences you have quoted in your question are right and which ones are wrong.
Your sentence #1a is clearly incorrect. But other sentences are correct.