There is no limit to how many people can be sponsored by the same person; the difficulty comes in when looking at the financial requirements.
All sponsored immigrants will need to be listed for purposes of calculating household size and income. I strongly recommend that he speaks with an immigration attorney.
There's also the possibility that his current wife will sue him for support using the I-864 (assuming she's not dead, has not naturalized, has not abandoned her residency or has not earned enough qualifying SS quarters).
On a purely practical note, you need to tread carefully here - jk makes some very valid points.

