[Mackers]

Frame/fork look late 70s early 80s to me.
1966 probably refers to someone becoming world champion on a Bottecchia in that year.

A lot of its value will depend on correctly identifying tubing and components (from what I can see Campagnolo Victory or Triomphe from ~1985)

Rear pre-cspc quick release would indicate <1978.

Seat post size can be a good indicator of tube quality/prestige.

I'd keep my expectations low, the Bottecchia name was not always synonymous with quality

 

[Mackers]

I think your brother picked up parts here and there and added and replaced as he went along.

Front derailleur is a post cspc Nuovo Record with the standard band which puts it mid 80s.
Crankset is a Victory from the mid 80s
The wheels have been relaced with somewhat modern rims to what I assume are the original hubs, maybe Nuovo Tipo/Gran Sport, very hard to date those without looking inside. The year is stamped in the cones.
Shifter levers are Records from the early 80s.