Can immigration maintain an old priority date for the cases i will file for my son and daughter?

The general answer is no. Their status as a derivative ends when you can no longer immigrate through that petition. Your marriage creates an impediment. There 'may have been' other visa options for your 19 year old. This, where an experienced immigration and visa attorney handled this matter before your marriage. However, the facts are unclear, so there may have been complications.

Although the petition, of concern, 'may conceivably help' your children for other foreseeable purposes, it cannot help them now. You should hold on to the I-797 approval form, among other documentation. When the visa is current, the NVC will notify you or your mother (where you update your address). The children should look to other possible visa options.

I strongly recommend that you contact a candid and experienced immigration attorney like our office.

The above is general information not meant to be legal advice. This response does not create an attorney-client relationship.