Two sensors using I2C
Yes, that's the idea behind bus protocols like i2c. You only require the sensors on i2c to have different bus adresses. A sensor's address usually can be chosen by soldering a jumper (the mpu6050 provides this feature on pin AD0). If you can't avoid an address collision you could use an i2c multiplexer or a microcontroller in between the sensor and the actual mcu (but probably that's not neccessary when using only two sensors).

Using SPI and I2C at the same time is absolutely no problem on the atmega!