@UserAccount  
Well then, with all these restrictions you are placing on me, I would have to do something that may seem kind of villainous. I do not have the right to choose which one lives and which one dies.
 
They are not my parents.
 
I would have to take all three Apple siblings with me and have them vote on which one of their parents they want to save. With all three of them there, I only need two of them to agree on which one of their parents to save. So, if two say dad, and only one says mom, I would have to save Bright Mac. And the third sibling would just have to live on resenting the other two and Bright Mac for the rest of their lives.
 
Or maybe all four of them would turn their ire onto me, for forcing this Sophie’s Choice-esque decision upon them.

I would save both of them || by getting rid of Granny(Annie) Smith and Grand Pear; let them get eaten by timeberwolves or somehow kicked out of Ponyville by themselves ||.

i would

Save both and have a threesome

@Neko Majin C  
No, you do the math about the events of every single moment of their lives and what it will do to the universe. Every single decision would alter the timeline too significantly and destroy the entire universe. Only by swooping in one minute before they die and taking one of them with you, can you save either of them. If you do anything more, the paradoxes will be way too huge. You talk to all the top scientists and biggest geniuses in the world and they all agree, this is the only possible option. It’s one or none.

@UserAccount  
I could save them both if I go back just far enough to see what leads to their deaths and how they die and then go back even further to change several different things to force them to make different decisions, ultimately leading them down a path where they do not die. Hell, I might not even need to do that first part. The details of their deaths have to be a part of some public records somewhere.

@Background Pony #4291  
This

@Neko Majin C  
You can only save one due to a law about paradoxes that you discover that states that the universe will be destroyed if you go back more than once.

If I invented time travel why would I only be able to save one of them? If I can travel through time and I can only save one of them, I can save one at a time. Save one of them, go back in time again, save the other. Simple as that. Also, if I invented time travel, I would not waste it on saving fictional characters from death. I would use it for something more worthwhile.

Oh, absolutely, I would.  
With Bright Mac.