Is there a wyt ti'n as well as a rwyt ti'n? If so, what's the difference?
I believe that you drop the r when it's a question. Don't quote me on that though.
Rwt ti is the singular informal. Dych chi is the plural and formal (of both plural and singular)
Is gweithio used for all pronouns, or does it change its form with the various prounouns, like, I, he, etc.?
I don't think it changes in this form. The pronoun at the front changes 'dwi'n gweithio' 'rwyt ti'n gweithio' etc.
See the course notes for explanations and examples.
- mewn - in somewhere/thing general or unspecified - mewn car; mewn tŷ (in a car; in a house)
- yn/yng/ym - in somewhere/thing specific - ym Mangor; yn y car; yng nghar Dewi (in Bangor; in the car; in Dewi's car)
To see how to find the course notes - at the top of this page click on 'Topic: Welsh', then on 'Popular', and then look for the sticky discussion 'Course hints and tips'.
That I don't know. Prepositions always mess me up. Hopefully someone who is fluent jumps on and can answer that for you.