How are estate profits divided if only some or one of the heirs invested either time or money in improving it? What are the factors that affect the law? When are some exceptions to the rules?

It was customary that a father who married off his oldest son in a house adjacent to his own house, would give that house to the son as a gift. Since this was the generally accepted practice, even if the father didn't specify it as a gift to the son, the law presumes that the house was given to the son. This is one of three laws that are declared "A halakha without a clear explanation."

If brothers are living off the father's estate, in what situation would a brother's salary be shared with the other brothers? Are doctor bills for one of the heirs paid for by the estate? The Gemara differentiates between those who get sick because they brought it upon themselves and those who get sick due to circumstances beyond their control.

Reciprocal marriage gifts (which were common in those days and could be demanded in a court) - how are they divided among heirs? On what do those laws depend?