Someone present two places at the same time - real story

This is a event my family talks about and it happened with one of my cousins:

On 24 June 2004 my cousins were gathered at my grandmothers house. This is an very large and old house bought by my grandfather about 50 years ago, it's said that there used to be a graveyard where the house stands now, many of my personal and family paranormal experiences have occurred here. That day one of my cousins experienced one very vivid and real paranormal event, it was so real that he was unaware it had happened until about two months later, when he learned that my elder step sister (who lives in another city) hadn't even been to our city in over a year.
When he came to know this at a causal family discussion he became pale to death, he said it was impossible because that day (2 months earlier) he had chatted with her (alone) for about an hour in the dinning room of my grandmothers house !

Another short experience happened to myself when i was only 7. All us brothers and sisters (5 of us) were playing hide n seek with kids who's house was just opposite our grandmothers (our house at that time), their house was also old and big like ours. During that play something weird happened, my little sis was the one seeking and rest of us were hiding. I was hiding in a two way corridor, i was actually just standing at the junction of two long corridors  which had glass doors at their ends. I saw my little sis approaching on of the glass doors from the outside, so i turned at started to run towards the other glass door but before i could do that I saw my little sis standing behind the other glass door as well !

The Investigation:
 We did a bit of digging found some interesting culprits.
Here's a list of possible paranormal beings/creatures which can change form and appear as someone else:
1. Skin walkers/ Shape shifters :  These were the ones which we were particularly interested in because the main focus of these supernatural beings is to transmogrify (change form).  Mostly they change into animal forms but they can even take on human forms.
The Navajo people are among those to describe the skin walkers or as they say "yee naaldlooshii", they used to believe that such powers of shape changing are acquired by those who commit social taboos (for more info check this wiki article: skin walkers).
Shape shifters appear more in European folklore and literature, such shape shifting abilities are even demonstrated in modern day books and movies like the 'Harry Potter series' (where they appear as 'Animagi') and 'The Spiderwick Chronicles' (for more info read this wiki on Shape Shifters).


2. Changelings: These are mythical creatures mostly from western European folklore, these usually appear in the form of human children. Usually some supernatural creature like a fairy or elf has replaced a human child with a changeling. More info at this wiki: Changelings


3. Jinn: In our local almost every paranormal event can be attributed to this single creature as it has many powers including the power to change form. This was the first explanation I got from an elder when I told him my story of seeing my sister in two places. Here's a great article on the topic: Jinn


4. Angels: We can all agree that Angles have been mentioned all over time and space in my writings and almost always they appear in human like forms and they have powers to do almost anything.


A few questions still remain like why do such beings exist and why would any of these beings want to take on the forms of my sisters or for that matter whats the motive behind anything these beings do?

Suppose if you had such powers what would have you done and why?