Bonjour Alexandre. If I understood right your kid was born when you were not married yet. In that case the family court can decide that you are leagally the father of the kid IF the time period between the birth of the kid and your marriage is not too long. What is the time period...I don't know. I am struggling with the same problem.
> My Scottish friend uses this company and he says they are very professional (hmmm...well...even if using Gmail address :-) ). However, you can ask for their opinion and quotation. But don't say anything about the immigration in Udon, just ask how you could get the marriage visa.
Can you try some other immigration office ? Or even an agency ? I suppose an agency can arrange it easily, even the marriage visa. Of course, it is more expensive but certainly cheaper than fly to Finland and back to Thailand.
I came to Thailand 9th of March and now stuck here. I should go to Vietnam to work. However the immigration in Roi Et has been very helpful and as I wrote earlier, there are no problems to extend my tourist visa for 2 months after 26.9.
I was today at Roi Et immigration. Because I am married with Thai having 2 kids with her I can extend my tourist visa after 26.9. two months paying 1900 bht. I think you don't need to go to Finland for marriage visa. You can get that visa from Thailand, but you must have 400.000bht in your bank account or monthly income minimum 40.000 to get marriage visa.