You can run 2 pumps to increase your head height but they should be run in Series, not parallel, if the goal is to increase head height. Pumps in parallel will increase your flow rate by 2, but it will not increase the head height by the same factor. If you run them in series, it will increase the head height by 2, but not double the flow rate.
It is important that if running in series, the pumps are sized the same.
In other words you want 1 tube...
1st pump output connected to second pump input.