I've learn that if the direct object of a VN is a pronoun, you use the possessive construction if the object with the VN . So, the sentence above would be:
"Dw i ddim yn dy gredu di" or, in something more colloquial, at least one of those possessive pronouns would remain plus its appropriate mutation, if any.
Am I mistaken? Here, it just seems that the subject pronoun is placed after the verb, English positioning-style.
What I think I've leant:
Dw i'n dy garu di - I love you Dan ni'n eich gweld chi - we see you
What the sentence above suggests: Dw i'n caru ti Dan ni'n gweld chi
It should definitely be 'dw i ddim yn dy gredu di'. I have no idea why the pronoun has been dropped; it is not optional, it must be there. As a native speaker, I find there many simple errors in the course worrying.
Remember that this course is still in Beta - we're here to help clean up the mistakes before it gets promoted. So far, this course has taught me more about Welsh grammar than Welsh lessons in an English-medium school from age 5-15. Not bad for only being live for a few months.
But thank you for the clarification about Welsh grammar. Any time I come across a mistake like this I'll report it from now on.