[General] You can sing along with them.

[Silverobama]

Judy was a newcomer of our English club meeting. She said she would go to the English club tonight. Maybe it was her first time to join us so she was a bit shy. Every Monday night we sing songs together. In order to encourage her and make her feel less nervous, I said:

You can sing along with them. (I wasn't at the English club meeting.)

The intended meaning is: You can sing songs with those participants together and you'll feel less nervous.

Is the italic sentence natural?

 

[Tarheel]

Is the italic sentence natural?

It's natural enough. However, I might have said:

They'll be singing songs tonight. Feel free to join in.

 

[Rover_KE]

Most shy people would be horrified at being asked to sing with a bunch of strangers.

 

[5jj]

If I started to sing with a group of strangers, the room would be empty within a minute.

 

[Tdol]

You can sing along/join in would do for me.