If someone filed one of my dependants and my me e-file was rejected so I mailed my return forms in,what is the next step I need to take? Will I get my refund back?

If someone already claimed your dependents via their efile which is whys yours got rejected... once they receive your paper tax returns will audit you and the other person who claimed your dependent. you will most likely have to send papers proving they are dependents and the other person fraud by claiming them (like court documents, dependents school records (same address as you), etc). then IRS will give you your refund.

Also this other person does not even have a job to claim taxes on my childre are going to school from my mother's address so our address will not be the same but I provide all living expenses and all financial expenses.

most likely they had someone else claim the children for them and will give them the money from the return. as long as your name is on their school information or you have court documents you will be fine.

No she actually claim the child herself thru a bogus tax agent

not sure how she did that if she doesn't work you have to have a W2, 1098 or 1099 to file  taxes. but as long as you have all the information when they audit you will get the return. it will just take a while.