How do I find the left side of the sets as the following example?

o = {3, 2};
g = {9};
z = {5, 7};
f = {8, 11};

I'd like the result to be:

I would like a code to do this even if I change or add more definitions to the sets list freely, for example adding two more sets or renaming some.

My attempt to accomplish this (although believe that must have a much easier way):

ClearAll["Global`*"]

o = {3, 2};
g = {9};
z = {5, 7};
f = {8, 11};

FromLetterNumber[
 Select[Flatten[
   Table[If[
     Length[Flatten[
        Take[Position[
          Table[If[
            FromDigits[
              Flatten[
               Take[Alphabet[] // ToExpression, {ii}]]] \[Element] 
             Reals, 1], {ii, 1, 26}], 1], {ii}]]] < 2, 
     Take[Position[
       Table[If[
         FromDigits[
           Flatten[
            Take[Alphabet[] // ToExpression, {ii}]]] \[Element] Reals,
          1], {ii, 1, 26}], 1], {ii}]], {ii, 1, 26}]], NumberQ]]

My achievement was partial, because the answer is not organized correctly in a way that I want (instead, it was in alphabetic sort). Is there any way to do that with a smarter code? Would someone please know how to help me?

Thanks.