I've known several military men with a medical discharge (chemical imbalance of the brain, as it were) that, due to their medical condition, were not very spit or polished. Not saying that is the case here, just that it could be possible.
You're absolutely right.
I regretted typing that out as stereotyping right after I wrote it. ;-p Like you, I can think of several reasons (and friends) who are more 'Harley' and less 'boots shined & buzzcut trim' these days.
Good call with the chemical imbalance point, too. Several mood and personality disorders can feature crashes, psychotic breaks, sudden paranoia. If he was often chipper and up, and has suddenly flipped out, there may be a diagnosis in play that we're not aware of.
Or maybe he's just a crappy arse whose gone on a selfish rampage of the 'if I can't have you, no one else will either' sort.
Both plausible, and it doesn't look great for the girls either way.
We have to assume that the girls are under a lot of duress. If he's shuffling them around, perhaps even breaking into homes as some have theorized, that brings mixed hope for them. They might be thinking, "Maybe someone will discover the break in and rescue us!" He'd either have to dismantle any of the electronic devices in the area, or keep them tied up for extended periods of time.
If he is keeping them in a vehicle, like an SUV, that brings cramped quarters and a lot of difficulty when they need food & bathroom breaks. Not easy.
8, 12, and 14 y/o are old enough to be smart & creative, but he's potentially using threats to harm the other siblings as a method of control. Which must be a stunning shock to them, as this is obviously someone they've trusted and had fun with, based on the pictures on FB.
Aside from the fear of possibly not knowing where their Mom is, and missing home & Dad(s), they're dealing with this sudden head trip of trust shattered by an older 'friend'.
No matter how we look at it, this is extraordinarily difficult for these little girls.