If the employees have less than one year’s service, there is no problem in sacking them. But if they have been in your employment for more than 12 months, you should at least examine the risk of an unfair dismissal claim.
The Acas code states that misconduct outside of work should not be treated as an automatic reason for dismissal. The main consideration should be whether the offence makes workers unsuitable for their type of work.
It is hard to see how this incident would affect the employees’ ability to work. But if a local paper got hold of the story, for example, a tribunal might take a different view, as the company could be seen as condoning their behaviour if it did not take action.