السلام عليكم ورحمة الله وبركاته
1. In Islam, parts severed from a living body deserve the same respect accorded to a deceased body.
2. Such respect is demonstrated through burial, preferably in a cemetery, but also acceptable in any clean area.
3. Incineration of severed body parts would be incompatible with the required respect.
4. There are a few points on which the disposal of severed body parts differ with the ritual burial of a deceased body:
4.1 The disposal of severed body parts is not accompanied by any specific ritual procedures.
4.2 There is no specific time limit for the disposal of severed body parts.
4.3 The burial of corpses is obligatory, whereas the burial of severed body parts is
preferable.
5. Against this backing, the answers to your specific questions are as follows:
5.1 There are no specific time limits to the disposal of severed body parts whether they be samples, organs, limbs or foetuses.
5.2 Miscarried foetuses should preferably be buried either in a cemetery or in any clean piece of earth. Incinerating them is incompatible with the respect they ought to be shown.
5.3 It is permissible to bury tissues from different people in one grave.
والله تعالى أعلم
And Allāh knows best
Issued: October 2018