If they finish within the top 2, then they can qualify for the main tournament. Only other team (apart from Turkey) who can spoil Croatia's chances is Wales. They are one of the most under-rated teams within UEFA and on their day they can make life difficult even for stronger sides such as England and France. But I don't know how they are going to perform this time, especially after the retirement of Gareth Bale. The other teams in that group (Armenia and Latvia) are there just to make up the numbers. During recent times, their quality has gone down and I don't think that they stand any chance against teams like Croatia, Turkey and Wales.
I know than first two spots in the group lead to the final tournament. But my opinion is that it's not the same to finish first or second. Finishing at the first place boosts team's morale and their synergy with the fans. I remember the time when Croatian fans were not so interested in the national team. Then Dalic was appointed as the manager and they started winning strong teams again. Now the stadiums are again full when the national team is playing.
At least on paper, Croatia is much stronger than Turkey and Wales. The other two (Latvia and Armenia) are there just to make up the numbers. And then chances of any upsets are low, because each team will face others two times in the group phase. Even if one of the underdogs win one match by luck, the higher ranked team has another chance to get back at them. In two weeks, Croatia will be playing their first match, against Wales (they will be having the home advantage, since the match is scheduled to be held at the Stadion Poljud in Split). And on 28th they have a tough match, against Turkey.
Yes, you said it right, on paper Croatia is better than both Wales and Turkey, but Croatia has always had big problems with weaker national teams in qualifying for major competitions.
The qualification for the last European Championship started with a defeat against Slovenia, and the qualification for the League of Nations with a defeat against Austria at home.
After that defeat against Austria, Croatia beat both France and Denmark away from home, so it was once again shown that Croatia always plays the best against the strongest national teams and always has serious problems against weaker teams.
I don't know if this is due to the mentality of the Croatian players, underestimating the opponent or some other reason, but I expect similar problems in these qualifications as well.