Transfer of Title: Bought from Private-Party but Title Was Never Transferred

My question involves a consumer law issue in the State of: Texas

I purchased a classic Mustang recently, at the time of sale we didn't not finalize the bill of sale. The seller and I lived very close by so I assumed we would just finish it the next day. However he moved further away now (not too far ~100miles), and hasn't been so helpful. While looking at the title I noticed it was never fully transferred in his name. The Name on the front is from the original owner. They did fill out the top back of the title, listing both the previous owners name & signature and his. Still need to fill out the bill of sale, and 130-u form. I have the title and receipts of registration from the first owner. This being my first purchase privately I'm confused on how to go about this. Please help.

Do I have him (2nd seller) complete a title transfer in his name first?

Can the 2nd seller and me just go to the DMV and work it out?

If the 2nd seller refuses to help out can I sue/take legal action?

Thanks

Transfer of Title: Bought from Private-Party but Title Was Never Transferred