Getting that true ending where both sun jian and sun ce make it through is actually pretty interesting, and i've found a reliable way to make it happen. For the xiangyang battle, you'll want to break away from the main fight right at the start and make your way to the southwestern area, where there's this creepy fog-covered forest. Once you take down that phantom zhang jiao lurking there, you need to reach sun jian before huang gai does - you'll know you got it right when you see that "fate altered" pop up.

The really tricky part comes during the suppression of wu battle though, and i learned this one the hard way. First thing you gotta do is keep sun quan safe by securing those nearby bases, then when sun ce heads into that western forest, follow him to the southwest corner. There's this hidden cave entrance behind some vines that's pretty easy to miss, but once you find it and beat bailuan inside, you'll get another one of those "fate altered" messages which is exactly what we want.

After you've changed both of those events, just finish up the campaign like normal. Just between us though, might want to level up a bit and grab some decent weapons first, cause the timing on some of these events can be pretty tight if you're not prepared for it.