the vibration produced in the coil of a speaker is due to current passing through it hence it obey ohms law
the watts for 2 ohms is more than 4 ohms. depending on the ohms your speakers take up and the wattage the speakers use, tells you what size amp you need.
There are 4 ohms
wire two 8 ohm speakers in a parallel circuit!
The wattage and ohms of a speaker are not related; the resistance for speakers is usually 4 or 8 ohms.
What is the ohms capacity
Yes they are
No. Two 16 ohm speakers connected together are either 32 ohms, if wired in series, or 8 ohms, if wired in parallel. You can, however, connect four 16 ohm speakers in series-parallel to get 16 ohms, with four times the power handling capacity of just one.
4 ohms
Use 5.2 ohms, which is the closest to 8 ohms.
There is no single standard. Many computer speakers are rated at 8 ohms while others are 16 ohms or higher. My computer subwoofer here is 4 ohms.
I presume you mean wired to four ohms amplifier output: In this case, pair the two speakers in in series which will make the give you 18 Ohms and then join the two pairs in parallel which will result in approximately eight ohms. Then connect then in that format to the amplifier. It will work for you.
Car stereos use 12V which is lower than the 30V used in home stereos. Power = voltage^2/Resistance. To get the same power with lower voltage the speaker resistance is lower. Most home speakers are now 4 Ohms and car speakers are now 2 Ohms.