Dr. Jonathan Rosman in the Journal of Halacha (here, p. 42) brings a gemara in Baba Batra 154a as a source that a family has a special obligation not to desecrate a body
The Gemara in Bava Batra discusses a case where a father dies and
leaves property to his son. The son immediately sells the property and
soon after dies as well. The son’s inheritors claim that the deceased
had not reached adulthood and therefore the sale should be void and
the property should belong to the father’s other heirs. The buyers
claim that the deceased had reached adulthood, thus the sale is
legally binding and the property therefore belongs to them. Rabbi
Akiva was asked whether it would be permitted to exhume the body to
see if the deceased had physical signs of adulthood.
Rabbi Akiva answered that the body should not be examined because of
nivul hamet, or desecration of the dead. Rabbi Akiva further added
that after death signs of puberty change and are unreliable in
determining adulthood, and therefore examining the body would not be
Tosafot state that Rabbi Akiva was compelled to provide both answers
because there are cases where it would have been permissible to
examine the body. Tosafot write that the buyers have the right to
examine the body since they stand to lose money. Financial loss is a
permissible reason to examine the body, according to Tosafot.
However, suggest Tosafot, the family has a special obligation to the deceased and thus even for financial loss cannot degrade the body.
Therefore, Rabbi Akiva had to bring the second answer that even for
the buyers who are permitted to defile the body because of financial
loss, examining the body would not help because signs of puberty
change after death. According to Tosafot, the prohibition of nivul
hamet applies only when there is no good reason to defile the
deceased; but for an acceptable purpose, such as monetary loss, nivul
hamet would not apply.
Although you are correct that a doctor son can treat his father if he is the only one (or the best one) to do so (MT Hilkhot Mamrim 5:7 or here on MY), in the context of an autopsy it is difficult to imagine one couldn't bring a second specialist since there is less urgency.