Velicí is always prounounced as velicí, only in the nonstandard Common Czech one can use use veliký even for masculine animate nominative plural.
For the standard Czech declension see https://en.wiktionary.org/wiki/velik%C3%BD#Declension
ć does not exist in Czech
velcí and velicí are two equivalent forms used for the masculine animate gender
velké and veliké is used for the feminine gender and the masculine inanimate gender
velká and veliká is used for the neuter gender
All the above is for the nominative case. With more cases you will see there will be more forms.