Write a speech for my sons' wedding

I am the father of the groom and I have been told I will be giving the primary speech at the wedding dinner. For reason i choose not to go into detail about at this time I expect there to be an above average amount of tension at this wedding because of some family conflicts . both my former wife and i are remarried and it has not been a perfect blending between the two couples. In addition i know very little about the bride and the bride's family. I am thinking I would like much of my "speech" to be humorous. Frankly I am hoping to lighten up the mood and I am hoping I can entertain the audience. I am looking for an end result somewhere between 5 and 7 minutes long. I guess it could be slightly shorter or possibly a little longer but I do not want to overstay my welcome.