"Do I need to take them to see a Psychologist? Does every parent go trough this? Is it a phase that will pass? "
To an extent each child may act out at times. If you find that this is a chronic occurrence with the twins that is causing significant distress/disruptiveness, then it is a good idea to have them evaluated by a psychologist to determine what is causing the behavior. Then, if it is a diagnosable condition ex: ODD, they'd offer appropriate tools to deal with this and work with both of them and with you- the parents.
It may be helpful to find a setting where in addition to individual counseling, family and group therapy is available. Behavior is generally purposeful. Something is not only triggering the behavior but it is also allowing them to continue to act that way. A clinician would look at all of the different factors ex- is the behavior taking place only at home or at other places ex: school, at grandparent's homes, camp, etc. The behavior may also be as a result of how the process/integrate information and their inability to cope well with certain stimuli in their environment. That is why it is appropriate at this point to seek professional assistance for them to cover all of your basis. You've mentioned that they do not respond well to consequences at home.
We live near Louis Trichardt in the Limpopo Province, about 150km from Polokwane/ Pietersburg. Can you recommend someone in this are who can help me?
What is the zip code?
I did not realize you're in SA. I'm in the US and do not know of anyone personally there. Sorry I'd opt out as the initial question did not ask for referral but for feedback. There is a list of the approved clinicians http://www.psychotherapy.co.za/GeckoLinks.asp?TYP=6