Seating availability in J
 

Is there a way to find what seats are available for Business class on EK 20 on
the 31st December, as I am flying with two grandchildren and would like to be certain we will be together ie in front or behind us for them

You can use Expert Flyer to get the seat map, No subscription required.

You can just also make a booking on the Emirates website and just look at the seat map before you purchase

Has anyone else found the seat map in Expert Flyer to be very unreliable recently? I made a booking in J (with mrs t) yesterday with was a bit based on availability of our favourite rows and when it came to picking the seats after finalising the booking, the availability was very different. Tried via EK chat function but they confirm that those seats are not available. Has a similar situation with an F seat a few months ago (available on EF but not on MMB), but there the chat agent cleared it for me.
Obviously can't set seat alerts for the ones I want as EF shows them as open..... Bit of a first world problem, but I expect EF to be accurate.

What was different? EF was showing seats as available but they were actually unavailable? I have found the seat maps on EF to be quite reliable. Recently I got
a notification that a window opened up on a 388 in J
about two hours before the flight. I asked the lounge agent to move me into it. She said it was taken but after showing her the EF screen she "refreshed" something and voila I was in the seat!

Yes, that's exactly what was (and still is) happening. EF shows lots of empty seats, MMB shows them occupied (or rather 'unavailable'). That's why I tried the chat function (asked for the seats I wanted) and the agent said they were unavailable.
I had an F booking in September, where EH showed a seat available and on MMB it was not. In that instance the chat agent immediately moved me to that seat.
My earlier experience with EF is that the seat maps are relatively reliable.