i don't want to assert what's correct and incorrect, but basically, these are things that naturally come in pairs and therefore are referred to, just like in english, in plural (unless of course you're talking about a single thing)... աչք, հոնք, ձեռք, ոտք, կուրծք, ծնողք, etc (can't think of other words at this point), ք being the plurative suffix... since over the time եր [er] and ներ [ner] have become the dominant prurative suffixes (the only i would say), աչք (etc) has lost its meaning as 'eyes' and has become an 'eye'... therefore, the use of աչքեր has come forward... some of the mentioned words have transformed differently than others... for example, it's կրծքեր and not կուրծեր, but it's ծնողներ and not ծնողքներ... (i guess this one is because it's a lot more common to talk about a single parent than about a single breast... unless you're telling someone 'tsitsikd utem' )
all three forms that you mentioned are used today in different contexts, and i can't tell what's right or wrong, but the formal ea usage for the mentioned words is as follows:
sng - plr
աչք - աչքեր
հոնք - հոնքեր
ձեռք - ձեռքեր
ոտք - ոտքեր
կուրծք - կրծքեր
ծնող - ծնողներ
it's interesting to note that there are other things which do not come in pairs, but are still referred to in plural... and not only in armenian but also in english... for example, երկինք (although this word in modern wa and ea is also singular, just like the rest of the words above), the skies...
but, i'm sure there are many better posts about this in the forum that you can find by searching one of the words above...
just to make another point, in the examples that you gave, it would be ձեոք ձեոՆեր ձեռքեր, as we discussed before...
it's also interesting to note that ականջ, ear, is not in this list of words... though an older word for it, ունկ[ն] can fit somewhere there i guess...
another word that just came to mind is շրթունք...
it's also interesting to mention that today ք is used for plural a lot more often in wa than in ea... and that many ea speakers, who are not interested in languages in general, get very surprised about ք being a plural suffix, yet ք, as such, is very common throughout our language, starting from pronouns, ex. մենք, դուք, նրանք to words such as գիրք...