OP, can I suggest whatever course of action you take that you try to keep your emotions out of it when dealing with them? I get the impression they are trying to placate you and force you into something you are not ready for. The best way to combat that is to take the higher ground, respond neutrally, so that they can't dismiss you as irrational / dramatic / emotional. Make it clear that any discussion on how you are feeling is to be between you and your family members. I've been there and it's a highly emotional situation, but if you focus on objective facts it's harder for them to try to push their agenda onto you. "I'm not interested" is much more effective than "I don't feel comfortable with that" or "I'm not ready because I'm still recovering from the divorce". Remember that you don't owe them anything. This is between you and your mother, you don't have a relationship with these people.
I still think the best course of action is to ignore them completely and deal only with your mother, but just wanted to include the above as based on their previous conduct it's possible they'll be forced upon you again. If I were you, I'd be inclined to say to my mother: "Mom, you know that I told you I may be ready in a few months to meet them but that now was too soon. These unsolicited messages from them make them seem pushy and quite frankly rude. I was serious about meeting them in a few months but now I'm not sure if I have any interested in meeting them whatsoever. Please tell them not to contact me again". Obviously you will meet them at some point if the relationship continues, but I think it's worth letting her know exactly how off-putting this incident is. Honestly I can't stop thinking about this thread, this situation really bothers me. Trying to force somebody a relationship onto somebody while they are still dealing with a highly emotional family situation just seems.... so wrong.