The 8 GB modules might work together with the existing 4 GB modules. This is dependent on whether respective module characteristics (apart from voltage, frequency, and timings) are similar enough to allow inter-module compatibility. The only way to be sure is to test them. Some adjustment of settings in BIOS may also be required to help the modules work together.
Also, to maximize memory bandwidth, the recommended configuration of memory is to have the same (total) memory capacity in each channel. So there should be an 8 GB module and a 4 GB module in each channel (making 12 GB per channel) making a total of 24 GB of system memory.
The first two memory slots form the first channel, and the last two slots form the second channel.
The 1 GB module might be compatible with the other modules, but again this depends on its' characteristics. In any case, if using two 8 GB modules and two 4 GB modules, then all four memory slots will be occupied, so the 1 GB module can't be installed.