I recently learned that when my ex remarried she may have changed my sons' last names to her new husbands. (I have reason to suspect this was before they turned 18 and I believe he adopted them, although I've never signed anything. Is this legal?) I have been paying child support and actually continued past the court mandated 18years/high school until one son was 21 and the other 20. I am a disabled Vet (100%) and my sons' college tuitions have been paid for by the VA because of my disability status. When I decided to stop sending money (which I am not ordered to do so, since they are over 18, I received a very nasty letter from the ex. ) Is it legal for her current husband to adopt and have my sons take his last name without my permission? Thank you.

No its not. If an adoption was done, you should be able to check court records to find out. However, there may not have been a legal name change. The children could have just started using their step father's name wherever they wanted.

I doubt that an adoption occurred because you would have had to be contacted. If you were paying court ordered support there would have been a record of it.