Yes, I'm sure they fit.
Externally, the ink cartridges do not differ. Normal, XL or XXL differ only in the filling quantity. In other words, the "normal" ink cartridges are "half empty". The XXL are full.
I have a TS9150 and have used different fill levels. Fits without any problems.
A quick look at Canon.de shows that the i-SENSYS MF651CW is a colour laser and requires Canon 067(H) toner cartridges. Please check again yourself, but they are also available here.
According to my research, there is currently no multipack from Canon.
Multipacks are currently only available as compatible cartridges. I have no experience with Amazon cartridges.
Depending on the Canon model, different tank sizes are required. Your model probably also has 2 tanks with the colour black. A narrow tank with the no. CLI-581 and a wide tank with the no. PGI-580.
Apart from their respective part numbers, both cartridges have the same capacity and compatibility. It is likely that in the long term we will only offer one of the two (availability from suppliers).
Prices are based on supply and demand, suppliers and availability of goods. If you want to make a complaint about this, please contact customer service, the Community is not for that :)
Unfortunately I can't say for sure, I own a TS6350.
According to Canon https://store.canon.de/pixma-ts-8..., however, the CLI-571x are installed in the TS8050 and not the CLI-581x series shown here.