These are issues that may get fermented, leading to industrial disputes if not handled at the right time. If the workers work on Sundays/holidays, they have to be given a compensatory holiday. You can regulate the compensatory off by stating that any holiday worked or any comp off earned shall be availed within one/two months.
The claim that employees get sick on every outstation work cannot be allowed. There cannot be separate rules for those who conduct outstation tours and those who are permanently stationed in the office. Similarly, being away from one's native place or family is not a matter for the company. As far as the organization is concerned, the functioning of the organization is paramount. If employees wish to be in their native places, they can opt for that but after leaving the company. If you allow such demands, why wouldn't you expect a demand that the company itself should be shifted to their native place!
Today's job market is highly competitive, such that if employees leave, the employer will lose nothing but will easily find a replacement. However, once an employee loses their job, finding a similar job elsewhere in the same industry becomes challenging because all employers, at least within the same industry, know each other, allowing for cross-references about any employee. This can easily reveal the reasons behind why someone left a company or why they were let go. Try to convince your employees about this reality. I believe that an informal talk followed by an official communication will serve the purpose.
Regards,
Madhu.T.K