Can you put 2 8 ohm's speakers in 1 channel?

Your simplest scheme would be to wire them in series - one after the other - thus presenting a 16 ohm load to the amplifier. This will cause no harm to the amplifier.

If you wired them in parallel, then the effective load would be only 4 ohms, and this would cause more load on the amplifier. Depending upon the design of your amplifier, this could cause more distortion.

In closing, it is only in the 'mid range' that the impedance of the speaker is the nominal load - say 8 ohm. At 'resonance' - generally at frequencies of a few tens of Hertz, the impedance of your speaker will be a few times its nominal impedance. At high frequencies, again the impedance of the speaker will increase to a few times nominal.