Portraiture just isn't my thing

[g-fi]

Two words, open shade. The light is a little harsh in the last two and the WB issues with the first two have been mentioned. I think you're soft in the first ones because of the low light, if you shoot another indoor location like this, get them closer to a source of natural light, or add in some fill.

Portraiture is not easy, and it's not for everyone. I feel the same way about landscape photography, I just can't do it. I'd much rather shoot photos of people rather than try and figure out how to shoot a landscape. Having said that, it's not rocket science either. Playing around with positioning and brush up on the basics of posing people in front of a camera. Be mindful of your backgrounds, things shooting out of people's heads, running through the picture, etc. It's so easy to forget those little details until later when you're done shooting. Look at other examples of engagement pictures to get a good idea of what is flattering vs. what isn't. Good graphic backgrounds are preferable to a common busy background. Think outside of the box about showing the relationship between two people rather than "Client A and B smiling and looking at the camera".

And HAVE FUN!