As PP have said, take a step back from helping to plan your shower. This is a gift to you and if your hostess is inclined to ask for your input, this is when it should be given.
As for the Hall vs Restaurant debate, well if your In-Laws are not paying, then they are not hosting, regardless of any help they may offer to the hostess. The hostess, in this case, is your mother. Let her know that you are happy with whatever venue she chooses and take a moment to thank her for offering to host this and let her know how much you appreciate her generosity.
I truly hope this whole issue isn't making your mother feel as if she is throwing an inferior shower, simply because you have outspoken and ungrateful in-laws.