DCISS no longer provides family invitation letters for visitor visas (B-1/B-2). The U.S. Department of State does not consider invitation letters when determining whether to issue or deny the visa:
" Visa applicants must qualify on the basis of the applicant's residence and ties abroad, rather than assurances from U.S. family and friends. A letter of invitation or Affidavit of Support is not needed to apply for a visitor visa. If you choose to bring a letter of invitation or Affidavit of Support to your interview, please remember it is not one of the factors used in determining whether to issue or deny the visa. " - https://travel.state.gov/content/travel/en/us-visas/tourism-visit/visitor.html
Students who would like to write their own invitation letters for their family members can use the Sample Invitation Letter template here .