Since you are planning to use different impedances of speakers connected in parallel directly to the amp, rather than using a speaker switcher/selector with impedance compensation (such as Niles), you would have to make sure your total impedance (the one the amp sees when connected to all the speakers) is not drop below a safe level for the amp, otherwise it would overheat and shutdown, especially at high volume levels driving all the speakers at once; heat reduces the life of your equipment and you run the chance to even kill it.
Here is formula that you could use to calculate total impedance in ohms for paraller speakers (+ connected to +, and - connected to -):
(Sp1 x Sp2) / (Sp1 + Sp2) = Total impedance the amp faces
For example: 2 pairs of 8ohm and 8ohm connected in parallel would be:
(8x8) / (8+8) = 64/16 = 4 ohms which is low enough for many amps/receivers
If using 4ohm speakers:
(4x4) / (4+4) = 16/8 = 2 ohms, you may fry eggs on your amp before it shuts down.
Add more speakers in parallel, and/or lower the individual sp ohms, and the total ohms drops further, a number closer to zero is short circuit between the + and - speaker connectors in back of your amp.
Some people cheat the formula and puts some speakers "in series" combined with "in parallel" because when they are in series (the + of one speaker going to the - of the next one) they add impedance (resistance) to the final number while the parallel reduces it, but the sonic balance of such approach is not as good as the impedance problem it solves on the amp, plus you have no control of individual volume levels.
If you have an all-over-the-house parallel speaker installation that is already done I recommend a good speaker switcher/selector with individual volume control and impedance matching per speaker (such as Niles), and connect the amp to it so it will see a balanced impedance regardless which speaker is on and at what volume.
Rodolfo La Maestra