Meeting half-siblings ...

So he was with your mother around the same time that he was with his current wife? If she doesn't know about your birth mother or you, then I would think that he wouldn't be eager to bring that up to her. If she does know about your birth mother and you then again I wouldn't think that he'd be eager to bring that up to her. It's all water under the bridge but emotions are not always logical and jealousy would certainly be a prime emotion in this situation. If you contact one of the kids and they call mom and say "Mom, did you know dad had another kid by someone else?" can you imagine the storm that could erupt? I'd ask your birth dad again but in this situation I'd never contact them directly. Is it fair to you? No. We often get the short end of the stick.Is it fair to your 3 half sibs? Probably not. Is it fair to maybe throw the relationship between your birth father and his wife into a possible tailspin? I don't think so. Probably not what you want to hear, but I'd make this his call. At least let him know that you know who they are and would like to get to know them. Just my opinion though.