You need to use a video modulator. Cables with RCA connectors go between the DVD player and the modulator. Then a cable with F connectors goes from the modulator to a 75 to 300 ohm balun transformer that converts to twinlead that connects to the TV terminals. I have a RCA modulator but I don't think those are available now.
https://www.amazon.com/GE-RF-Modulat...3960697&sr=8-2
You should get a modulator like this now, they put out a old NTSC analog signal.
At some point only the modulators that do digital will be available, those will not work with vintage TVs.
There may be something mis-wired on that TV. Do you have an oscilloscope?
Maybe the deflection frequencies are far off or badly distorted. Maybe the video detector is installed backwards. The sync separator might be fowled up. A scope could help sort it out. Have you checked the voltages in the deflection circuits?