Hello Edward,

No, these chargers can not be stacked. They are inherently buck regulators and will need a consistent ground between the input source the battery cathode (negative terminal).

Most of TI's chargers are configured to step the input voltage down to the battery voltage.

With a 5V input you would first need a boosting stage to create an intermediate rail at a voltage above the stacked regulation voltage of your pack. The next stage should be one of the many multi-cell chargers that TI has available.

I would recommend looking into the WEBENCH tool to design the boosting stage:

http://www.ti.com/lsds/ti/analog/webench/power.page

The using the parametric search select the right multi-cell charger:

http://www.ti.com/lsds/ti/power-management/battery-charger-solutions-products.page#o4=ACTIVE&p338=Li-Ion;Li-Polymer&p1152=2-4%20Cells&p1498=Catalog