
sepa'a means 'similar to' not means 'together' not 'with'?
english translation must be like ' please sing similar to me' (imitate my sining). what's true?

"X sings with Y." (X kantas kun Y.) means that X's act of singing is parallel to Y's (La X-a faro de kanti paralelas je la Y-a.).
parallel to Y = fi'o se panra Y / se pa'a Y
Other possible translations:
pe'u do sanga fi'o se kansa mi
pe'u do joi mi sanga
ko joi mi sanga

{pe'u} eats {sanga}.
{pe'u do sanga sepa'a mi} or just {pe'u do sanga pa'a mi}