Listening to the latest mix and not reading the other posts (so I don't know what was addressed, fresh mind on this one
).
Bring up the guitars and once that's done you'll need to bring up the vocals a tad. Add some reverb and compress those vocals a tad more. Solid recording and playing. Vocalist needs to build his confidence, he sounds like he's holding back too much. Do they write on acoustic then play it together? If the vocalist was forced to "do more" in the song's writing stage he would be more likely to come up with parts that forces him to be more into the song. It sounds like he's relying on the rest of the band to do all the work. Should be the other way around, at least in most rock bands
. Guess what I'm saying is the vocals should be more emotive!
As an engineer you could be a powerful voice of objectivity and motivation in the studio. It's your choice, but I know I try to help people along - push them to be the best they can. Most of the time people are open to new ideas. In the cases that they're not it's very likely they aren't going to get far because as we all know music and the crafting of it is an ongoing learning curve. Most of that curve is climbed with the help of other's input and lots of practice.