Massive headache time, I send my wishes to you.
If you have a good case then you should be ok. I can't see why a judge would prevent your plans to improve your childs future especially as "father" has been absent for so long :!:
How does your son feel, regarding his "father" trying to prevent him going?
If your son wants to migrate then the court should and would take into consideration your son's "true wishes and feelings"
Could your son write to "father" and express his wishes and feelings?
How do you feel your solicitor is performing?
To save cost, could you go L.I.P. with a McKenzie friend?
My heart goes out to you both, it's a very sensitive situation especially for your son.
Good luck
Al.