OP, if you are still around:
I do not agree with your POV with regard to men, they are lovely and great fathers many of them
Other than that, I think you are not being unreasonable.
Buying a lovely suit for a little boy is completely cool, especially with a bow tie, bow ties are very cool for little boys.
Having a child-free wedding is riddiculous, and especially banning babies is beyond riddiculous.
Your husband is best man, but first and foremost he is a father, that must always come first.
I think your concern for your lovely MIL is legitimate, more and more so reading your updates. Someone said that 68 is not frail, but with all due respect that is very individual. Some are fit as a fiddle at 90, others are frail long before time. I suspect you are a better judge of your MIL's condition than us reading and commenting on your thread, so I trust your assessment on what might be a bit too much for her.
Your husband sounds like he has not quite taken onboard the responsibility of being a parent. I cannot see why he can't leave early with you. I am sure the groom will be able to get through the wedding night without your husband's handholding.