What skills should be in your team? All the skills needed to get from “Idea” to “Done”. Organizations tend to be organized around functions or skill sets, e.g. a development team, a test team, and operations team etc.
This usually causes dependencies: you can’t do this piece of work until that piece of work is finished. If you are having dependences, try borrowing the skill(s) from the other team(s) for a few sprints and see if your velocity does not improve.