HaRav Moshe Feinstein has an extensive Teshuva in Igros Moshe Even HaEzer vol 4 Siman 60 where he concludes that this precise situation would absolutely be forbidden Min HaTorah.

You should continue following the customs your father and grandfather observed. The essence of a Minhag is continuing one’s parent’s practices; as no one can know with certainty what was the “original” Minhag.

The simplest solution would be to designate one Kaddish for the cousin and a different one for you grandparent.

First of all, assuming you are Ashkenazi and had already eaten a kzayis of bread before stepping outside, you do not need to make a new Beracha when you continue your meal.

Regarding washing, if you only went out of the house for a moment and intended to return, you do not need to wash again. However, if there was a prolonged delay and you were completely distracted from maintaining the cleanliness of your hand, the Biur Halacha writes that you are required to wash a second time and recite a new Beracha of Al Netilas Yadayim.

The Mishna Berura 25§14 writes that even though the Gemara calls someone who Davens without Tefilin מעיד עדות שקר בעצמו, this only refers to someone who did so out of negligence and laziness. However, someone who did not have access to Tefillin at the proper time certainly should not delay reciting Kriyas Shema at the proper time.

Generally, all food products, including spices, should be certified. The intricacies of modern food production can create unimaginable issues with seemingly innocuous ingredients. Nevertheless, there are some spices which can be used without certification. The following link contains a chart of which do and don't. http://www.crcweb.org/spice_list.php