Is it possible for my friend’s marriage to be restored after a khula/talaq due to sifli ilm?

I have a question regarding ruju after khula/talaq in relation to my friend’s marriage. Actually boy was not having any intention to give her talaq thinking that it is a big sin but girl’s family members asked for talaq thinking that boy is not suitable/fit for his wife. In talaqnama some text was written which has meaning that due to dissimilar nature of both and despite convincing each other finally it is not possible to live together for both. They have returned all things of each other and boy has given talaq to the girl. And after talaq they can marry wherever they want and not having any pending claims for further action. After 5-6 months (iddah passed) of talaq, they knew that all this was due to attack of sifli ilm and started to morn for what they have done in past. Weather it is possible to get back to married life again after suitable treatment of that sifli ilm. Whether it was khula/single talaq or 3 talaqs have taken place. Please explain in details.