Try and find out the motives behind your ex's friends reaching out to you. If it's to plot a way of getting you guys back together, then don't give room for them to succeed but if they are just reaching out to you for old times sake, then there is nothing to worry about.

I'm sorry to hear that you are dealing with a breakup. I don't think that her friends are contacting you on purpose, maybe is just a horrible coincidence.
However, when you don't feel well you need your space to recover yourself before helping others. I think you could be nice and honest and tell to her friends that you need some space, that you appreciate the friendship but right now you need to be alone sometime to put your ideas in order and to work in your personal projects. Tell them that you will contact them later but right now you need to focus in your stuff.
Think it this way, you are not been mean, but you need to keep going on your life and if something or someone is stopping you to do it then you are free to tell them that you need your space. Some people will understand that and some people will not but that's their choice, you don't need to please them and they should have more tact to know that you need some time alone.