if pistons 1 3 4 and 6 are at TDC all together it's because something in the motor has gone horribly horribly wrong
generally, firing order on an inline six is 1, 5, 3, 6, 2, 4, but remebering that they are paired together, so that 1 and 6 are at the same position in the bore as each other, 2 and 5, 3 and 4 so on. it's the camshaft that determines whether or not each piston at TDC (Top dead centre, or the highest point in the bore) is actually at it's compression stroke or exhgaust stroke.
remember folks, it's Compression, Ignition, Combustion, Exhaust (Or Suck, Squeeze, Bang, Blow if thats easier to remember )
The V means the motor is in a V shape, with 3 pistons on each side. this makes it easier to fit in small engine bays, but the downside is they vibrate and therefore engine harmonics is poor. This can be compensated with a balance shaft or a bloody big harmonic balancer on the front to soak up the vibration. it also takes a lot more machining to make and can be expensive.
an inline motor, all pistons are in a line one after the other. an inline motor is very bulky and needs a long engine bay. but vibration is minimal, except with big revs, when the crank can actually start to flop around like a skipping rope. again a harmonic balancer is used if the motor is prone to this. (modern motors dont usually have this problem anymore, it's mainly old motors with big crank journal spacing that did this)