Is it really important what Ms. Manners has to say about it? I think it is up to the people whose names are on the marriage contract to decide. Discuss it with your spouse.
Yes it is etiquette to have a bridal shower for a second wedding.
Yes. It is proper etiquette, although it is also common for them to decline (but that probably depends on your relationship with him/her).
If you have not been invited to the wedding then you should not send a gift.
No, it is not proper etiquette to send weddinginvitations by email if it is a large wedding. If you are having a small wedding and it's casual then you could send a card invitation by email.
There is a proper etiquette for changing diapers out in public which includes one not throwing the diapers out in public but one should take the diapers home to dispose of and one should only change diapers in a bathroom.
* Whether some guests are going to a wedding or not it is etiquette to send them a wedding invitation as some people are sentimental and will keep the invitation.
Bring a card or small token gift.
Ask the bride if it is ok, unless you want it to be a surprise. Then, ask the groom if it is ok.
cancel freaking wedding
* The best thing to do when someone does not buy a wedding gift for your son or daughter's wedding is to ignore it. Some of these guests may well give a wedding gift later and those that don't then they have no etiquette and just remember that when it's their turn if one of their children gets married. It's not worth the energy to bring it up and is not proper etiquette to do so.
Be yourself
The website Thankster has a plethora of information and tips on writing thank you notes from your wedding. The site gives many ideas and sentiments that you can include in the note along with proper etiquette.