Normally I would say just go by the chart because the weight goes up rather quickly, however since you have a short time to make progress just go with what feels right.
Also, gonna post a series on bench form that may be helpful, not a different routine just some coaching pointers that may help you and your sons increase their bench. Some people say the change in form alone leads to strength gains.
http://train.elitefts.com/instructio...ench-parts1-7/