"rather unbelievable" is a perfectly valid phrase in written English, and can be used to describe something that is very difficult to believe.
For example, "It is rather unbelievable that the tiny country managed to conquer its larger neighbor."
Events took a rather unbelievable course.
'Eating above the clouds is rather unbelievable'.
He recalled his reaction, saying, "I thought it is rather unbelievable".
"Dan Cochran, from the unresolved warranty department of VF, Eagle Creek's parent company, called to say they would replace the backpack," Ms. Jahrling wrote on Sept. 9. "He claimed he knew nothing of your column — rather unbelievable since it has been two months since I last heard from anyone connected to the company.
In 2009, in a rather unbelievable opinion, a Fisa judge stated that court-ordered privacy protections – that were supposed to be in place for years – were "so frequently and systematically violated" by the NSA "that it can fairly be said that this critical element of the overall … [surveillance] regime has never functioned effectively".
It makes me think of those gruesome and rather unbelievable fairy tales.
It is unbelievable, and rather fun".
Rather, they are usually unbelievable stories in which his performance is completely over the top.
You may not get room service or a terry cloth robe, but what Airbnb vacation rentals lack in amenities, they make up for in unbelievable, sometimes rather bizarre experiences.
Not only was the Sun in the throes of a campaign against domestic violence, but in an EastEnders style plot twist (ie, wholly unbelievable and rather hammily overdone), Steve McFadden, who plays Grant's brother Phil, was allegedly assaulted by his ex-girlfriend on the same night.
Rather, he is under the unbelievable pressure from a surging team that has been getting better with each race.
