In order.
1. Koutetsu no Daitenshi
2. Daitenshi ni Sasageru Uta
3. Doutei Saizensen
4. Bed no Shita no Himitsu
Harem Nights and Family Visits are side stories, but they are about all the couples from 1. to 2. so its better to read them after 2.
Next time if you are not sure about if the manga has prequels, sequels, spinoffs or side stories or not, you can just check the info page of that manga on bakaupdates.
Can someone give me a more specific order of this series of story??? This particular couple has mutiple DJs so I'm not sure which I should read first or next or what.