Reading the following threads may be helpful (and avoid repetition).
and
Assuming that the original investor is a spouse/parent, and he/she achieves citizenship, then there may be no reason to continue GV as the dependents can apply for citizenship via ther relationship with the main investor (naturalisation via marriage or birth - see below).
Naturalisation can be via marriage: If you are married to a Portuguese citizen you may obtain Portuguese citizenship after three years as long as you make your declaration while you remain married.
Naturalisation via birth if born outside of Portugal with a parent of Portuguese nationality (ie citizen)
Naturalisation by residence: Minimum residence period of 5 years.
The following link is to the Ministry of Justice which gives the rules and deals with applications: https://justica.gov.pt/Registos/Nacionalidade/Nacionalidade-portuguesa#Quempodeternacionalidadeportuguesa. The relevant information is in Portuguese. There are other requirements for citizenship, including a clear police record & language - all on the Ministry of Justice site.