If they believe in one Toheed and not committing serious crimes, they are practicing Muslims, even if they are not taking care of Allahs obligations, such as prayer or fasting. Sometimes we think if someone doesn’t pray or fast they are not Muslims or atleast not practicing Muslims.
My suggestion to bring such people more closer to Islam is the same as you teach a child. What it means is that you do not just give direct advice and lecture. You first become an example yourself and impress the person with your performance. Also, you never tell the person that he is wrong or never give a surcastic remark, but ask the right questions for which the answers will automatically lead to a desired conclusion.
Find opportunities to spend more time with such person, impress the person with your speech and actions and also convey your message as in general conversation, as part of conversation or a story of someone else. Don’t rush and give it a lot of time. It will work. You can also explore in general conversation what bothers such person regarding religion and address their specific issue. Finding bottom line issue is a key and it is very difficult to find out unless the person really likes and trust you. Normally they will tell you some other reason than the real reason.