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Comments:

 An example of a case-marker would be "yaar˜o yaa-sˆyaa wˆ maalˆmins
 littaaf“i", (the boy bought the teacher a book, where "wˆ" is marking
 teacher "maalˆmins" as the indirect object).

This example doesn't parse :(

 I changed my head-opt-subject-phrase (which only functions with the
 sentence-final question marker) so that it would only take a main
 clause verb, or in other words a non-head-dtr with an inflected verb
 (not infinitive).

I assume you mean head-dtr, since head-opt-subj is a unary rule
(and therefor has no non-head-dtr).  I don't understand why this
rule is currently constraining the CASE of the subject, though. 
I think that constraint probably isn't having any effect.

 Now the CASE nom pronoun "I and the boy went to the market" (nii dˆ
 yaar˜o mun-jee kˆasuwaa) will parse, but the CASE dat won't (min“ dˆ
 yaar˜o mun-jee kˆasuwaa).

Nice :-)