I wouldn't feed 14week old pullets laying mash. I'd stick with an All Flock/Flock Raiser or Chick Start that has low Calcium and high protein (18-22%).
If they are with the adults already, just feed the Adult the All Flock or Chick Starter, providing oyster shell free choice.
At that age, I'd treat for Coccidiosis and deworm.
Liquid Corid dose is 2tsp or Powdered Corid Dose is 1 1/2tsp per gallon of water given for 5-7 days as the only source of drinking water.
Do not add any extra vitamins/electrolytes that contain B1(Thiamine) to food or water during the course of treatment.
To treat most worms that poultry can have except for Tapeworm you can use Safeguard (Fenbendazole) or Valbazen (Albendazole). Both are given orally by weight; they do not mix well with water.
Safeguard dose is 0.23ml per pound of weight given orally once a day for 5 days in a row.
---OR---
Valbazen dose is 0.08ml per pound of weight given orally once, then repeated in 10 days
Here's how to give oral medications:
https://www.backyardchickens.com/ar...dications-to-all-poultry-and-waterfowl.73335/