Driving LED with parallel current sources
Yes, you can parallel current sources to get a combined current source that is the sum of the two.  This is analogous to putting voltage sources in series to get a combined source that is the sum of the two voltages.

There is no issue of balancing the current sources.  Each will sink the current it is set to sink.  There is nothing wrong, for example, with combining 5 mA and 20 mA current sources to make a 25 mA current source.

One issue to watch out for is the compliance range of each current source.  That is the voltage over which a current source still works like a current source.  The voltage the two current sources settle at must be within the compliance range of both sources.  If it's not, then at least one of them isn't a current source anymore.