FLR M Querry - re Non Accompanying Child

[Nellyb1979]

Hello,
Im starting to put the application together for my wifes FLR M extension (first one), ive had a look at the questions and they appear to be similar but a lot more in depth then the leave to enter visa. One question ive come stuck with is regards to her son who is 17 lives with my wives parents in Thailand and is not coming to the UK.

The question is asking us for his birth certificate which is fine i assume we will have to get this translated, but the question is also asking about her sons dad who lives elsewhere. whilst relations arent quite UK - russia type relations with the childs father they arent at the level in which the father will give his address to me and he certainly wont give us any utility bills or similar to confirm where he lives. how do we approach the answer to this one, because we know his name (i think he is on the birth certificate), but if we say that we know him it asks for this information, if we click dont know it doesnt ask for this information but essentially we are lying?

any help with this is appreciated.
thanks