If you have extra work engage the same employees overtime and pay overtime wages until the project is over. Alternatively, employ new persons for a fixed term till the project is over. Once the project is over, their employment terminates automatically. No need to provide alternative employment nor compensation.
The second option is the best one because by asking the employees to do overtime, you may not be able to get the desired result due to various reasons, like, you cannot compel employees to work overtime and as such you cannot expect them doing overtime especially on weekends and the first day of the week, as per statute there is a maximum overtime hours per month or per quarter and you cannot cross it. Moreover the overtime wages should be at double the average rate of salary.
It is always desirable to hire people on fixed term contract specifying that the employment is for a fixed period and the same will be terminated once the project is over.