Is it possible to connect one motor between M1 and M2 terminals to increase maxium current supplied to this motor?
Hello.
No, in general connecting H-bridges in parallel like that presents the risk of the VIN and GND rails being connected together through a low resistance path, which can damage your system very quickly. There are some motor drivers that have provisions for using more than one channel in parallel to provide more current, but you should not do that with our high-power motor drivers.
-Nathan