"With your father?"
अनुवाद:तुम्हारे पिता के साथ?
Normally, पिता takes respectful plural almost every time but there is not any rules. "आपके पिताओं के साथ" sounds very wrong because पिता is always singular. It will be as strange as hearing "with your fathers". Whereas the formation of this type for other masculine plural is perfectly okay such as in "आपके चाचाओं के साथ" i.e. "with your uncles" .
In the third person when we use 'is' ,"वह एक लड़का है" is used. In 3rd person normal nominative-like form is used. Perhaps, the reason is a strange class of sentences in Hindi.
In English, We say "There is a problem" when we mean 'There exists a problem' rather than "A problem is present over there." In short, those sentences where 'There' is used to imply existence instead of location at some distance. their parallel Hindi sentences have a special trait. Problem = समस्या in Hindi. 'समस्या है' (taking care of S-V-O orders etc) will be 'is problem' literally. But this imply (i.e. it's translation is) "There is problem." Taking consideration of 'a' in sentence as 'एक'. So 'there is a problem' translates to 'एक समस्या है'. Gist is 'Forget 'there' present in English sentence and translate as you do normally. (They will certainly add a skill covering this topic if they make a Hindi for English course.)
Back to topic, 'लड़का है' means 'There is boy'. Here 'लड़का' is in nominative like existence being sole noun in sentence. In 3rd person, we change 'there' with 'he', 'there is boy' turns into 'he is boy', boy's state is unchanged. In Hindi, we just add 'वह' for 'he' and boy's state here is again unchanged (nominative like existence ). it becomes 'वह एक लड़का है'.
Now for clarifications, this overriding of oblique by nominative happen when 1) it has possibility of use 'there' 2) related to 'is/am/are' stuff. 3) As a side note: 1st person also uses nominative like forms (I am a boy=मैं एक लड़का हूँ).
It may be confusing. But there is a good news which will alleviate some burden. Oblique case of all masculine word not ending with vowel 'आ' is same as nominative, Oblique case of all feminine word same as nominative. Also, Oblique form many masculine word ending with vowel 'आ' same as nominative. (there is some rules regarding oblique plural forms,but we don't need to think of that as Overriding will happen for all plurals in above cases.).
All these, sounds strange but things get simple after some experience (I may get mistaken at some points, I thinks it's mostly correct. They don't teach Hindi here as taught in foreign language program. I get puzzled myself often when I think about my native language.)
Wow. Thank you so much for that explanation, that clarifies things a lot. Just to confirm, when you say that overriding happens for plurals, that would mean that "you are boys" would come out as something like "तुम लोग लड़के हो," with लड़के this time being the nominative plural instead of the oblique singular?
It's nominative plural. Only case of where overriding not happens is masculine, 2nd person, singular number.