Hello
welcome to health care magic, I really appreciate your concern for your husband.
Soreness in stomach might be related to stomach
hyperacidity or
Acid reflux, another possibility is Acute
gastroenteritis or gut infection as such his stool is also stringy.
In my opinion he may require a course of antibiotics like ofloxacin or ornidazole group of drugs or its combination under medical supervision.
Meanwhile you can give him antiacidity medicines like
pantoprazole or ranitidine group of drugs or antacids.
Ask him to have plenty of fluids including ORS to counter
dehydration and electrolyte imbalances.
Curd and yoghurt will definitely help him which has probiotics property and helps in improving useful colonic flora.
Hope this answers your question, please do let me know if you have any more queries, I will gladly answer you.
Best wishes