Everybody sings in the local assembly. There is no place for a one-man show where somebody plays the piano and sings in front of the others. Neither a place for a team of five performing and showing their musical prowess in front of the whole congregation. The assembly is not a place to sit and watch a concert. An assembly gathering should be simple and serene, not with the beats and rhythms that only excite the emotions and the flesh.
The singing in the local assembly gathering is directed by the Holy Spirit alone. Hebrews 2:12 says,"...in the midst of the assembly [with all the brothers and sisters] will I [the Lord Jesus] sing praise to you [the Father]" (notice the Trinity involved). The Holy Spirit leads the way in the local assembly because it is an organism. It is living and spontaneous, not prearranged like the organizations and denominations. So, what song to sing and who will stand up to prompt the singing is unknown until the meeting is taking place.
"...singing and making melody in your heart to the Lord." Songs and melodies originate from the hearts of believers who are moved by the Holy Spirit, and flow openly in appreciation during the meeting. Everybody sings altogether with his/her own capacity. Some follow through the hymn books (a compilation of hymns), while others sing with their memory of the song. Every believers sing in one voice; all in the same level. Nobody is helmed. All sing to the Lord as one.