Ever wondered why our religion has a lot of "Gods" and yet claims there is only 1 God? Let me try to explain this with my own understanding.
In our culture and religion each God represents 1 function or more of the God. Like Saraswathy for Education, Laxmi for Wealth, Amman for health and so on. The reason behind this is when you approach God with a focused mind, more known as prayers, they will be answered. Therefore Hindus pray different Gods for different purposes. These Gods are situated in different kind of Temples for another reason. Each temples are built with different stone, metal and shapes to "catch" the "PROPER" Cosmic Energy and thats why when we go temples we feel different, clear mind is just 1 one them. That's why we can't put different Moorthis together in 1 temple as the effect will not be optimum.
Usually Malaysian Indians pray at Amman, Murugan, Vinayagar or Shivan Temples. As you already know, they are members of 1 family, Mother, Father and 2 Sons. Apart from this temples there are other temples like Mathurai Veeran, Aiyanar, Kali and so on. These are also known as Guardian Gods.
Normally when Indians conducts prayers like Thaipusam or Vinayagar Chaturthi, there will be chariots travels from the children Gods to the Parent God's Temples and show of respect and blessing just like us humans do get the blessing from our parents. Our Temples are not only representing our religion but also our culture. It reminds us to get blessing of our parents and only then we can success. This is just 1 example I can give you now.
Just like when we have problems (from unwanted people) we approach our King (in those days), but a King will not come personally to solve these troubles but he will summon the guard to look into it. When the problem is solved, we normally thank them (the guards) by giving whatever we can afford but never infront of the King.
Same goes to God, when we have unwanted trouble we approach our God. When we pray for help, the Guardian Gods will be summoned to help us by our main God. We normally thank these Guardian Gods by giving what they like most, or what we think he'll be happy with, like Mathurai Veeran is normally provided with beer and cigar, but these gifts can not be given in Amman temple eventhough Mathurai Veeran moorthis is located in Amman Temple.
When the King resides, the guards are to be present there but they have thier own houses and offices where we need to approach them. Same goes to these Guardian Gods.