Effects of connecting speakers in parallel vs series
As you say, don't connect your speakers in parallel, you might overload the amplifier.

Two speakers in series will sound a little quieter than a single speaker, for the same amplifier setting, but not very much. Although on paper the total power is halved, the ear is very non-linear to changes of level, and it will sound 'almost as loud', not 'half as loud'.

If the two loudspeakers have the same acoustic environment, then the damping factor will be no worse than for a single speaker.