Ok, my 2 cents since the question of add on card for magnus was asked.
For getting add-on card: (Easiest way)
You need to apply offline for getting Add on for magnus. When you apply, there is an option for giving details of your add on. Some axis personnel will tell you, "No need to apply now. Once you get the card, you can apply". But it is all bs. If you want add on, make sure they take their details and fill it. If not, then it is going to take a lot of work. If they don't allow you to add add-on details giving excuses, it is better to find another Axis agent if they won't come around. They have to fill in the details of your add on card member, and make sure to give an ID (preferably driving license of add on card holder- don't ask me why DL, why not aadhar or something. An Axis bank guy said submitting DL is easier to get an add-on card. I really do not know the answer to that). Then they will have to take photographs of both primary and add on card holder.
Regarding PP:
Only the primary card holder will get the PP for Magnus.
Regarding Regalia PP that was discussed, both PP (primary and secondary) can be used together. The total visits on both cards should be within the limit.
Also, for Magnus those who didn't apply for add-on card initially, I did see multiple DPs on people getting add-ons after pushing a few buttons.
The following link is on Axis bank website regarding add-on cards (I am leaving them over here, but I do not know if anyone was successful using the form or the method)
Axis Bank Credit Card Benefits - Know the various credit card benefits like auto debit facility, emi facility, add-on credit card and more.
www.axisbank.com