• Error in Schedule B of parent deed

I am Kumaran, based out of Chennai.I have a query regarding a settlement which was executed in my favour in Oct 2018 in Chennai. The nature of parent document is a sale deed. A single property having two documents, with a split up of 50% for each doc. One doc is registered is my mother's name and other document is registered as undivided equal half share in the name of my brother and myself. The schedule A is common for both the documents. In Oct 2018, two settlement deeds were executed in my favour, one from my mother and other from my brother. Now I have become 100% share holder of the property. The parent document which belongs to my brother and myself has a typographical error in the schedule-B in one of its boundaries ( the eastern boundary that divides mother's and our share is wrongly mentioned as the eastern boundary of A schedule but the description, layout plan and measurement of the plot are correctly specified in that parent deed, the same error has been carried forward in the settlement deed as well.Only after the execution of settlement deed we noticed the error in both settlement deed and its parent document. 

Parent document is a sale deed which is executed 25 years ago, so the vendors are not traceable to execute a rectification deed on parent document. I also don't wish to file a suit before Court under Section 26 of SPA 1963 as it is time consuming.

Could you please let me know what would be the best and optimal solution for getting the error corrected in the recently executed settlement deed.

Sub-registrar is advising to execute a unilateral self declaration stating the nature of problem in parent deed and principal deed, so that in future when any deed is executed for this document, the error can be rectified with this declaration deed.

Otherwise sub-registrar is suggesting to execute a rectification deed on the settlement deed with full stamp duty and registration charges.

My query is 

1. Can we simply execute a rectification deed on settlement deed with full stamp duty and registration charges, without rectifying the error on parent deed ? Is it valid ?

2. As per sub-registrar's advice, if I execute a self declaration and register it, it will not reflect in EC as the declaration comes under Book 4 and not Book 1. In such case, will this declaration has any effect ? 

3. Also I dont have patta for this property. Can I apply for patta with this self declaration deed ? will it be considered ?

4. If the above solution is not proper, could you please let me know what is the best solution