Deut. 13:2-4 (numbered 1-3 in Christian Bibles)
If there will arise among you a prophet, or a dreamer of a dream, and he gives you a sign or a wonder, and the sign or the wonder of which he spoke to you happens, [and he] says, "Let us go after other gods which you have not known, and let us worship them," you shall not heed the words of that prophet, or that dreamer of a dream; for the L-rd, your G-d, is testing you, to know whether you really love the L-rd, your G-d, with all your heart and with all your soul.
Judaism accepts that it is possible for someone to actually be able to produce a miracle and yet still be an evil-doer. The main proof of any would-be miracle worker's righteousness, is that his message not contradict the Torah.
Therefore, if in fact Jesus did exorcise demons, it is still possible that this was a test to see if the Jews would accept teachings contrary to the Torah. Rather than being a house divided, the evil pawns (demons) agreed to be removed in order to ensnare innocent souls into joining a new religion other than true Judaism. That is what a "test" of faith is, according to the Bible.
Since the OP is bringing Christian sources, (and although Jews do not believe in the New Testament) it is also proper to answer that the OP's question is easily solved even according to the New Testament.
Matthew 7:21-23 - The Sermon On The Mount: False Followers
"Not everyone who says to me, 'Lord, Lord,' will enter the kingdom of heaven, but he who does the will of my Father who is in heaven will enter. "Many will say to me on that day, 'Lord, Lord, did we not prophesy in your name, and in your name cast out demons, and in your name perform many miracles?' "And then I will declare to them, 'I never knew you; DEPART FROM ME, YOU WHO PRACTICE LAWLESSNESS.'
Here we see that Jesus himself does not accept the successful casting out of demons as a certain sign of the exorcist's righteousness. He actually says that casting out demons can be accomplished by people who practice lawlessness.
2 Thessalonians 2:9
The coming of the lawless one will be accompanied by the working of Satan, with every kind of power, sign, and false wonder.
So now we come full circle. If the NT agrees that the anti-christ is the "lawless one" and he is called "lawless" because that is how Satan works...and casting out demons can also be performed by lawless people...then ipso facto :) the NT just said that Satan also casts out demons!
So if Jesus knows this, why can't the Pharisees use this as an answer too??
It seems that the apostle Paul is also in agreement with this line of reasoning.
2 Corinthians 11: 12-15
But I will keep on doing what I am doing, in order to undercut those who want an opportunity to be regarded as our equals in the things they boast about. For such men are false apostles, deceitful workers, masquerading as apostles of Christ. And no wonder, for Satan himself masquerades as an angel of light. It is not surprising, then, if his servants masquerade as servants of righteousness. Their end will correspond to their actions.
If a demon (servant of Satan?) masquerades by pretending he is listening to the "righteous decree" of a true prophet, and running out of a victim's soul; then maybe the one telling him to leave is Satan pretending to be of the light?
There is no "house divided". It is just a con game. The NT tells us that Satan is capable of really good cons.
For false Christs and false prophets will appear and perform signs and wonders that would deceive even the elect, if that were possible.
So the Pharisees were just thinking what the New Testament was thinking all along. :)