If the STOP codon is in-frame with the ampicillin resistant gene coding sequence, one STOP codon should be able to stop the translation. To translate a bicistronic coding sequence (in your case, Chloramphenicol resistant gene), you will need a RBS in front of the ATG codon of the chloramphenicol resistant gene.
Retired academic researcher. Mention of a specific product does not imply my endorsement of the product. No conflict of interest or guarantee to work on the advice given. Do as I say, not as I do. Not liable to the loss of your valuable samples.