The /Ɵ/ sound is spelled with <th>. The /j/ sound is spelled with <y>.
This is a contrast between a voiceless dental and alveolar fricative and a voiced palatal semivowel, fairly close together in the mouth. It is not a problem.
Since the /Ɵ/ sound is of low frequency overall, the mean density value is low at 0.5%. The list makes 4 semantic distinctions, a loading of 33%.
thank yank thanked yanked thanking yanking thanks yanks thaw yaw thawed yawed thawing yawing thaws yaws thaw your thaws yours thorn yawn thorns yawns
John Higgins, Shaftesbury, November 2010.