By what you're describing, I assume you have paint on the outer edges of the door and the inside of the door frame. Paint doesn't make a good lubricant. And the door may not have been fitted to have the clearance for a coat of paint, or three coats if its an older house. And then when its humid and the door expands a bit, the paint rubs catches against the paint on the other surface.
If that is true, you could sand down or strip the offending parts until they clear each other without touching (and possibly repaint with a single coat if you need to). I'd expect sanding only to "rough it up" to increase the friction, not make it better.
There is no reason you cannot have conventional double doors on a closet.
Bracing the Inside Corner
To solve the free corner issue, you can put a small stop, attached to the floor at the center point between the two doors. It needs to be wide enought to stop both doors (probably anything over 1 inch would do) and tall enough to catch the doors at the bottom (3/4 or 1 inch should do, and you want it as short as practical).
The simplist approach is to use ordinary domed door stops screwed into the floor inside the closet. One could probably be placed to catch both doors. These may be prone to a toe stub, but are probably the least likely to cause harm.
If you want to make your own stop, you could use a metal L channel or a wooden block screwed through the top into the floor. Metal is smaller, but may be more prone to hurt if you stub your toe against it. A small wooden block with sloped shoulders might be better. It only needs to be thick enough to hold up (maybe 3/4 inches). All exposed edges sould be slightly rounded with sandpaper to soften the edges for safety.
Latching
The simplist approach to holding the doors closed is to use magnetic latches. You can put them at the top only or at the top and bottom. If you do put them on the bottom, put the latch on the door and the strike plate on the floor stopper (another reason to use a wooden stopper).
As an alternative, you could use a cabinet latch at the top.
Finally, you could use a button type latch set into the tops of each door and the door frame. These are somewhat harder to install, but look more finished.
Handles
In each of these cases, you would use dummy handles or pulls to open the doors.
Best Answer
With those rough opening sizes, I would have stepped up the door sizes a bit, 32" in a 34" r.o., and 38" in a 40" r.o. You need some space to plumb and level, but 4" is overkill. I tend to install the door as close as possible on the hinge side to the framing (shimming it out for plumb and possibly raising it a bit to keep the top level). I also use a few 3" screws through the hinges to reduce sagging, which also improves security. On the latch side, I shim behind the strike plate and dead bolt opening, and use 3" screws over there directly to the framing. Any door that doesn't have long screws into the framing is a higher risk for being kicked in, but that's honestly a majority of doors out there these days, security seems to be an upgrade.
For the jamb depth, if you can't find a door with the correct depth for your home, sometimes you can get a deeper jamb and cut it back with a table saw. But the easier solution is to get one a little too small and add a piece of filler trim on the inside to make the jamb flush with the drywall and the install the casing over that. I wouldn't even try to line that filler up perfectly to hide the seam, instead give it a 1/16-1/8" reveal and do the same with the casing on top of the filler. The multiple reveals will give it some depth and decent look where trying to conceal the seam is likely to result in an ugly gap appearing several months later.