Regarding Sabbath observance, this is different from inheritance law, because inheritance law comes to regulate division between one person and another (Even HaEzer / civil monetary law section), and there is nothing here that is between man and God (Yoreh De’ah / ritual law section). It seems strange to me that Jewish law would instruct its observers to get hurt at the expense of those who do not observe it.

As for a gift during one’s lifetime, sometimes a person dies suddenly before he has time to draw up an orderly will or think in an orderly way about his inheritance and how to circumvent the Torah’s inheritance laws. Sometimes the person leaving the inheritance is not even aware of the inheritance laws in Jewish law, because he himself is secular.

As for what you wrote here:
“Moreover, when there is a religious side and a secular side, someone who does not stipulate otherwise in advance can assume that the division will be according to civil law and not according to Jewish law, and perhaps it is considered as though he did make such a stipulation and gave it during his lifetime.”

Let us take a case as an example: a secular father dies suddenly, and he has a secular firstborn and a younger religious son. According to what you are saying, does it come out that the inheritance should be divided according to secular law in this case?

Inheritance law is between man and God. Therefore the halakhic decisors wrote that stipulating does not help here (only a gift during one’s lifetime does), and the law of the kingdom is the law does not apply here. This is not considered monetary law.
That is what follows according to the reasoning about stipulation. But I am not sure /.

But as a matter of fact, inheritance law appears in Choshen Mishpat. According to what you are saying, why is it there and not in Yoreh De’ah?

And another question: suppose we have a doubt in the law as to whom a certain part of the inheritance belongs, based on the reasoning you brought above that you are not sure about—does either side have presumptive possession of that particular part over which there is doubt? How is such presumptive possession determined? And if there is no presumptive possession, how does one resolve such a dispute in monetary law?

Because this is not like interest or charity, where the money does not legally belong to the injured party and there is only a halakhic obligation to give it to him. In inheritance, the money legally belongs to the heir; it is not merely that there is an obligation to give it to him. It is impossible not to give it to him. It is somewhat similar to a loan, as I explained in the column that dealt with it, where there is a commandment of repayment that turns into a legal lien.

I did not understand the question about presumptive possession. Are you asking which of the brothers has presumptive possession? None of them, of course.
There are very diverse rules about cases of doubt in monetary matters, both for a situation where there is presumptive possession and where there is not (such as “whoever is stronger prevails”). They divide it, judicial discretion, the burden of proof is on the claimant, let it remain in place, whoever is stronger prevails, etc. The medieval authorities discussed at great length when each such rule is applied.