A good, honest funeral director is worth his/her weight in gold in a situation like this. I have been involved, to one extent or another, in about 50 funerals. If there is a church connection, the minister should be more than willing to give advice, especially concerning the actual service. From what you said in your post it seems that your wife is carrying a tremendous load right now. By taking into consideration what you know of your FIL you might make suggestions that will help your wife. When planning there are several things to consider:

1) Financial resources available to pay for the funeral (don't let emotions override good judgment).

2) Travel time of friends or relatives who may want to attend will affect scheduling.

3) Availability of burial plots, crypts, or whatever final resting place you might choose (and the financial ramifications of obtaining such).

4) Does your MIL want to eventually be buried beside/near your FIL (this will affect the selection of a final resting place).

5) Since you are the one who may be able to remain the most "emotionally detached" you can be a great help to your wife by making sure that the funeral director fully explains each charge on the bill and why it is/may be necessary. If there is a viewing/wake/visitation at the funeral home that is an extra charge. If the funeral home chapel us used that is usually an extra charge. If the body is moved to another location (e.g. church building, home, etc.) the charge for that is separate. Opening and closing of the grave is usually charged by the cemetery but the funeral director will include it in the cost of the funeral unless you request otherwise. You get the picture.

As an earlier poster stated, the funeral is not really for the deceased. It is for those still living. If you can determine what your wife and her mother wants for him that would be a plus. You mentioned that your BIL is not helping even though he should be. That means he will probably complain about whatever is done, but if he doesn't help, in my opinion, he has no grounds to complain.

I have good connections with a couple of excellent funeral directors in this area but laws and customs differ from place to place. If I can offer anything helpful please feel free to contact me. Email is good.