Is the priority in inviting the people of areas where visiting graves and domes is prevalent exclusively for Tawhid (monotheism), or for Tawhid along with the rest of the matters of religion such as prayer? And what about those who do not commit polytheistic acts but commit some sins?

The state of those being invited must be considered in da'wah. Thus, whoever is a polytheist should be forbidden from shirk (definition) and commanded to Tawhid (definition), then to the rest of the commands of the religion. And whoever is a Muslim and has sins, should be forbidden from them and commanded to repent.