Anything wrong with connecting L298Ns in parallel?
I am not endorsing wiring the L298Ns in parallel, but simply discussing the issues involved, and how it might be accomplished. As others have pointed out, an easier solution is to purchase a more robust driver.
Simply wiring the L298Ns in parallel will cause problems.
A partial schematic of one of the motors, and one of the drivers, driven in one direction looks like this:



simulate this circuit &ndash; Schematic created using CircuitLab
With multiple drivers connected in parallel, a partial circuit would look like this:



simulate this circuit
A big problem with this arrangement is that the currents through the transistors may be unbalanced. Suppose Q2A is slightly warmer than Q2B or Q2C. It is likely to conduct more than 1/3 of the current. Conducting more current means that it will get hotter than Q2B and Q2C. Which will cause it conduct more of the current, etc.
If you are willing to trade some motor speed (voltage) for torque (current), you can balance the transistors to some extent by adding small value resistors between the transistors and the tie-points to the motor, like so:



simulate this circuit
The larger the resistors, the more voltage you will lose, and hence the lower the maximum rpm of your motor. However, the larger the resistor, the greater the current balance you can achieve. Sufficient balance, and you can safely connect multiple drivers to drive your motor, thus increasing your torque. However, this only works to a point. Obviously too large a value for the resistors, and you will lose more power in the resistors than you gain by having extra transistors.
You say that the two motors will require 4A combined. You don't say whether the motors will ever require more than 2A individually. (It could be that only one motor operates at a time, and when it does it requires 4A). I will assume that you only need 2A. (BTW the L298 is advertised as
capable of 4A total (for 2 drivers), so if the modules actually behaved as advertised, you could get the 4A out of a single module, but that is another story).
Assuming each transistor needs to conduct, say 0.7A, and you want, say 0.3V across each resistor, the resistor values should be 0.3/0.7 = 427m\$\Omega\$ or something in that vicinity. Although they should only dissipate 210mW, I would use 1/2 watt rated resistors. The resistors need to be matched. Tight tolerance 0.5\$\Omega\$, 0.5W resistors are commercially available.
That takes care of the issue of transistor balancing.
There is another issue that must be addressed. Shoot-through. If both transistors in a half-bridge are on simultaneously, shoot-through will occur. A large current will flow through the transistors without encountering the impedance of the motor. This is bad, so you want to ensure that shoot-through doesn't occur. By connecting the modules in parallel, you increase the possibility that a high side transistor in some module is on, while a low side transistor on the same side of the motor, but perhaps in a different module, is also on. It is important when changing voltage directions, that there is sufficient &quot;dead-time&quot;, so that all of the transistors are off, before any new transistor is turned on. It is your responsibility to ensure that.
Once again, I am only explaining how wiring the modules in parallel might be accomplished, but I am not endorsing this as a solution to the higher level problem of how to drive the motors.