The Ops' satement that they did this 1 or 2 times a week for 6 months and only when they were short of money equates to an admission of around 48 instances of fare evasion.
This is a serious matter and I strongly suggest that the OP wait to see what letter is received and what that letter alleges before contacting anyone.
Once a letter is received s/he will know the unique reference allocated to their case and who they are dealing with. I suggest that once that is received and if this letter alleges multiple instances of fare evasion, they may be asked to attend for a further interview under caution. If not, then they would be well advised to take the letter and speak with a qualified lawyer who specialises in criminal law. ( CAB do not generally fit that category)
There are many Solicitors who will give an initial consultation either free of charge, or for only a small fee.