There isn't much different these days to ற and ர - Jaffna Tamil there is a slight difference, but not noticable at all. "ஞ" and "ந" - the first is pronounced "nya" as in Enya (the singer) but the ny is pronounced together. The second is just a standard n sound. As a learner you should practice the difference between ழ, ல and ள - as these are very important.

ற மற்றும் ர are in Tamil kuril and nedil we can use it based on the sound ற nedil letter and ரis kuril letter for ற we can use it in மற்ற but ர can be used in மரம் not மறம் it's wrong ந used in நல்ல முறையில் ஞ is used in ஞானம் ந,ஞ are uyirezhuthu in Tamil language it's not kuril nedil these are different from each other

ற is harder 'ra'. When conjugated with itself , ற்ற is spelt as tra/drra. 'ர' is the normal one and is used most commonly. "ஞ" is ñ as in España. "ந" is again the normal n, mostly used.