How to put 2 or more fifos into 1 M9K in C3 device

The max width is 36 bits. The device handbook has all the details of what you can and can't do. Note that the muxing and routing into/out of the memory blocks is pretty expensive in silicon. It's easy to just think about number of bits, but number of ports and there size is a significant portion of how many you can put into a device. Altera has done stuff like 3 different memory sizes, including huge memories(512K on older devices), to try and accomodate different user requirements.