Is the weather in October better in Tenerife than Fuerteventura?
Very little difference. Most people who go to Tenerife base themselves in the South of the island which is warmer than the north. In Fuerteventura the holidaymakers spread themselves about a bit more. If you were to go to Corallejo in the north it would probably be a few degrees cooler than south Tenerife. If you went to Jandia it would be about the same.
Fuerteventura does tend to be a little windier than Tenerife so it can feel a little cooler.
Even so most places should see highs of mid 20’s in October.
Yes technically but only slightly. It should still be nice in Fuerteventura.