would octavia vrs seats fit by fabia vrs

Not without taking both apart and swapping all the Octavia bit over to the Fabia metal work.

That said I did a set of fronts recently in about an hour and a half.

3/4 of the rears you can do in a further half an hour but the large rear back rest section amended by an upholsterer to get it to fit the smaller metal work.

You'd also probably be better off buying a donor set of Fabia seats for the metal work so that your VRS seats are left complete and in a more saleable condition.

Have a search for "recaro" and you'll find a couple of threads detailing the process.