Shiva may be split depending on where the aveilim are and if they are coming to sit shiva in the same location together. There is a shita that the first yahrzeit is on the day of the kevura (1 year later obviously) and then the rest of the yahrzeits fall on the day of the petirah. That is how I observed aveilus for my parents, z”l.
I was not able to go to the beis aveilim for either because of being so far away. My mother, a”h, was niftar erev Pesach and the kevura was on the first day of Chol haMoed. Shiva was observed after Pesach was over and the first yahrzeit was during Pesach, after that on erev Pesach.
My father, z”l, was niftar on a Thursday night and I was notified on Friday morning. The kevura was not until Sunday morning. I was told by our Rav to begin sitting shiva immediately because I was not an onen and had no shaychus to the kevura, so I started immediately. My siblings began sitting shiva only after the kevura. Like with my mother, the first yahrzeit was on the day of the kevura and the following ones were on the day of the petirah.
I know of a big Rav who was niftar in America on a Thursday night/Friday morning. The levaya was first in America and then the rest of the levaya and the kevura were in EY. We found out that they got up from shiva on Wednesday. Apparently some family members stayed behind and started the shiva process so it ended earlier. I’m not really sure how that worked.