Reserving a tokaido shinkansen at Narita?

I will arrive at Narita airport at 19:00. Then i need to buy 2 different tickets at the airport. One from terminal1 to Shinagawa station using the NEX train tonight, Then a tokaido shinkansen from Shinagawa to Kyoto the next day in the very early morning. From where can i buy those two tickets?
Also, Can i buy a round trip tickets for the NEX and the shinkansen since I will return back in less than one week?
My problem is that I will arrive late in Narita and the information helpdesk services might be closed.

Would recommend JR Pass for your trip:
http://www.japanrailpass.net/en/about_jrp.html

Ticket counter/window is still open.

And from the ticket counter window at Narita airport i can buy a Nozomi from shinagawa to kyoto?

Yes

And is the ticket counter open till 10:00 PM? And is it crowded?

I think the ticket counter in Terminal 2 closes at 10 PM. You can make some reservations with JR East online at:

https://www.eki-net.com/pc/jreast-shinkansen-reservation/English/wb/co...

According to Hyperdia.com, the last NEX for Tokyo/Shinagawa departs at 21:46. If you're worried about your 19:00 arrival time being delayed, why not stay near Narita Airport on Night 1 and take an early morning NEX to Tokyo and then a Shinkansen to Kyoto to avoid the nighttime rush?

You can buy your tickets also at a ticket machine. Including the Nozomi ticket to Kyoto. You could even just buy that the next morning, or buy it in Shinagawa after you arrive there, if you are pressed for time at Narita.

19:00 arrival at Narita is not late.
Get the 4,000 yen round trip N'Ex ticket and your two shinkansen tickets for Tokyo-Kyoto return. roughly 28,000 yen for reserved seating or 26,000 yen non-reserved.
This is slightly higher than the 29,110 yen cost of the 7-day rail pass. That is seven calendar days from first use - you say your return is less than one week, so that is an option.

Many thanks for all your answers.
And those round trip tickets are doable from the ticketing machines? Or should be from the ticket office?

Round trip ticket is from ticket office/service center only. You need to show your non-Japanese passport.