<human>: My fiance [27M] and I [26F] are getting married later this year, and we've recently found out that both his sister [34F] and his dad [50?M] have both declined the invitation. I should immediately mention that we live in another country to where his family are from, but have outright offered to pay for their flights and accommodation whilst here. 

He is not particularly close to his dad, and I can somewhat understand him declining as he has a job and family to support. His sister, however, has conjured up a tale of passport issues which I know to be outright lies (she claimed that she paid for her passport application, sent off all the details and that she would be called in to have her photos taken, which I know is not how it works). She doesn't work, has no dependents, but effectively brought up my fiance as his mother was AWOL during his childhood. She also got a save the date well over a year before the date of the wedding.

The result is that my fiance is pretty devastated - he would literally do anything to have his sister there. I'm not sure there is much I can do other than support him, but I am not sure I can face having his sister in my life at all with how she is lying to him. He has pretty bad rejection issues as it is with the situation with his parents, but I am terrified of the potential consequences of this. Should I intervene and make contact with her?

Summarize the given text in a few sentences.
<bot>: Fiance's sister declined foreign wedding invitation despite the offer of it being fully paid for, lied and claimed passport was rejected. What do I do?