As a Catholic who has been married to the same woman for 45 years, I agree with this...
In the end we could only counsel them to "live as Catholic as they could," be active with the parish, frequently seek spiritual Communion with Our Lord, be patient, trust God, wait. Very difficult.
However, I can't see any alternative. I'm not sure the Church has the authority to OK bigamy. And I'd say this, I think, even if it were myself involved in this situation.
With all due respect, why would you want to influence others to sin by your bad counsel?