I can replace the bipolar capacitors with other not-polarized with the same technical values?

I forgot ..

the speakers date from 1992

I have used these and they sound good. These should work as long as they fit.
Of course, ideally you measure the ESR of each cap before replacing.

You can do this with a DATS unit or using Room EQ Wizard with a custom jig.

The 26 uF in the high pass doesn't make a lot of sense though. Are you sure?

Oh, OK, this makes more sense.  The 26 uF is on the mid range.

Be VERY careful replacing the 8uF that is in parallel on the mid. I'd need to do a full analysis, but if that has 2 Ohms or so of ESR, you don't want to remove it.