If it says 'Regrets Only' then you only RSVP if you can't go. So if you can go you are not required to tell the host anything.
It's not in most cases. Destination weddings may be an exception, but to invite someone to your shower and not your wedding is a big no no.
No. There is no rule of etiquette requiring you to invite a roommate to a baby shower. If it is a friend or relative, you will want to consider the impact that excluding this person would have on your relationship. If you are having a couples' or male & female shower, you need to invite this person if they are a significant other of a person that is invited.
Yeah, I would.
It is proper etiquette to only invite people to the shower who will also be invited to the wedding. If the couple is having a private ceremony with only family, then only invite family to the shower. If they are eloping and not inviting anyone, it would be safest not to have a shower because those at the shower would be expecting a wedding invitation.
Well..... you don't HAVE to but it's good to.
No, it is not in poor taste to give your daughter a baby shower. You could invite close relatives and a few of her friends to the baby shower.
On a general basis no, you do not invite out of town guests to a wedding shower if they live a fair ways away because it is just a half day event. They will bring you their wedding gift for you and your husband.
Just say "items such as bottles, pacifiers, diapers, etc. would be greatly appreciated" on the invite.
It's only appropriate if you invite me to join you
Declining a baby shower invitation should be done properly and delicately. For tips, see the related link below under "How do you decline a baby shower invitation".
If your unmarried daughter does not, of her own accord (without anyone interring) want to see her boyfriend again then the boyfriends mother should not invite 15 more people to the baby shower. If your daughter loves her boyfriend then there is no reason his mother should not be able to invite 15 of her friends, but, you can ask her to help out with the expenses.