I can imagine it was all pretty complicated to follow from a western, very precise bookkeeping point of view. A clash of cultures, if you will.
As I say, a lot of info we have comes from CIA cables released during various WIkileaks scandals and other non-classified documents and it's fair to say by the notes made from the Middle Eastern desks that they barely understand who is who and who does what.
Here's something to ponder - is Sheikh Mansour a powerful man?
Here's the Western view. Sheikh Mansour is the Vice President of the UAE, in addition to other duties such as the Deputy Prime Minister and Minster of Presidential Affairs which controls access to the President. Therefore he holds numerous positions of power and influence in an autocratic society.
Here's the UAE view. Sheikh Mansour is the son of Sheikh Zayed and one of the Bani Fatima brothers. He is not the head of his family and answers to MbZ totally and without qualification. The role given as DPM was negotiated during the formation of the country as being held by an Al Nahyan with the other tribes. Sheikh Mansour was made UAE Vice President, against the country's constitution, in order to punish the Al Maktoum family for embarrassing the UAE a decade earlier, for the Head of their family having his affairs dragged in court with his daughters which embarrassed the nation internationally, and to move Sheikh Mansour into more diplomatic conferences where he shines brighter. Abu Dhabi/the Al Nahyan are attempting to be treated as serious long term investors in the global markets and although still very loyal, they are starting to consider the Al Maktoums their troublesome backwater cousins who don't know how to behave and ruin their reputation akin to the Beverley Hillbillies. Sheikh Mansour was Western educated, is an ultra MbZ loyalist for historical and almost religious reasons (the Bani Fatima loyalty is based on a promise made to never attack your own family due to this happening in the past and it fucking up the tribe). He is not Sheikh Mansour in the structures of power. He is a person who exists to politically execute the will of MBZ.
Here's the CIA view. These people are nuts. Their power structures and inter-tribal loyalties and marriages and duties reference shit that happened 300 years ago on some random day in the desert where someone caught a falcon or some shit. Sheikh Mansour is an average C student in the US only noted because he liked NBA and football (soccer). He was quiet, not particularly outgoing or academic and mainly kept to himself while in the US outside a few incidents of awkwardness as a student. While MBZ got on with the job of becoming the next ruler, he mainly spaffed around with nature and conversation projects in his Government job and sports investment in his spare time. He really enjoys sport and the only thing he ever seemed to excel at was camel racing. He somewhat controversially got married to his first wife who was deemed unsuitable and quietly "retired from public life" until he married another woman with which he settled down and had kids. His first wife was an internal Abu Dhabi marriage to one of the "2 quarters" families mentioned before because they seemed to actually like each other from children. His second wife was a member of Dubai family which was right and proper and expected. Him and Khaldoon seem to be actual friends rather than Khaldoon and MbZ who have more of a employer-employee relationship. He's somewhat average, a bit head in the clouds at times unlike his very serious brothers who became leaders of military etc, but seems likeable to other leaders so did very well in diplomatic circles hence as an important brother, was given roles that suited his personality.
Essentially if you want to know if Mansour is powerful then it very much depends on your definition of what that means. By one view he has almost no political power at all. By another view he has almost complete political power. You can bias this however you want when writing about it.
I will say one thing - the "Abu Dhabi bought City to sportswash" thing to my understanding is the wrongest thing to ever be wrong in the history of wrongness. You can argue that's what we're used for now (and I don't agree) but to suggest that's why we're bought is totally incorrect. Sheikh Mansour just quite likes football. The UAE is a former British protectorate, it exists as a country due to help from the British, he grew up watching the BBC and whatever passes for MOTD on the World Service in the 70s and 80s. It has a strong British culture element to it and one of the best friends of Sheikh Zayed before he formed the UAE was a British explorer whose writings are now a major academic source for the landscape between the tribes at the time. It was noted in his time at University in the US that he enjoyed football. It was further noted that before his brother ascended to the crown and he was just the lesser important brother without too much to do in his 30s and 40s that decided to buy a football club which was brokered by one of the Dubai Hillbilly clan who then immediately set back their desire to be seen as serious businessmen rather than inept moneypots by 20 years. I can absolutely guarantee if MbZ knew about this at the time and understood how important to the reputation that a football club in the back arse of Manchester would become to the global reputation of Abu Dhabi and the UAE then he would have back handed his little brother and told him to grow up and stop playing games. City are now the most visible aspect of the Al Nahyan family, the thing that they are globally associated with more than any other business. Not to business leaders obviously but to the wider general public. Sheikh Mansour is not "the little brother of the leader", he is "that guy who owns Man City" which I'm sure is a source of real annoyance to MbZ and possibly one of great humour to Sheikh Mansour. If they had their way, these people would have absolutely nothing to do with us, but they're stuck with us now for the next several decades at least and they understand that they have to be successful.
Which member of the Bani Yas owns what and who gave what to who is so far off their radar in terms of importance and cheating that it beggars belief. Their State doesn't function in this manner.