Does writing on a will invalidate it?

Writing on a will does not invalidate the will. But....

Here is what happens:

If you cross something off a will it is removed. Thus the will once said Jane L Doe, It is now Jane Doe.

Are there several Jane Doe's in your family? If yes, then the will need to be corrected, continue reading:

Typically a Will must be signed by the testator, and witnessed by two disinterested witnesses. Since the addition of "J" applies to your sister it could be deemed invalid as she witnessed it. Additionally, there were not two witnesses.

You asked should the Will be rewritten. <I'm anticipating conflict among the heirs anyway and I don't want to provide any ammunition to challenge the will.> HUGE RED FLAG

I am unable to determine if the original will has actually been completed properly based on the info given. If there is sizable money involved here, then it would be best to consult with a Wills and Trust attorney ab properly drafted trust. At the very least a couple of hour to get the will done properly.

No. Your father and sister's correction method is considered normal on a contract, but not a will. But in either case it isn't necessary for the sake of an obvious clerical error. I suggest reprinting the will and signing with proper witnesses to be 100% certain.

You forgot to say where you are, so I will answer for English law because it's what I know.

Any correction on the face of a will is assumed to have been made later, so it isn't part of the will. However, there is no problem as long as it is clear who he meant. But to be completely safe, yes, it should be rewritten or amended by codicil.

No, writing a correction on the will does not invalidate the will.

Perfectly valid.

Unless the "L" is the correct middle initial for another real person in your family with the same name, you have no issue.

your father's attorney should, ideally, redraft the Will and have it properly witnessed.

No