Yes, traditionally one side of the church is filled with family and guests of the bride and her parents, and the other side with the family and guests of the Groom .
I think that it is more usual for some friends of the bride or groom's parents to host a shower or some of the bride's girlfriends but it is not improper for the groom's mother to host one if she would like. If there are other showers being given, I would not do another one if I were the groom's mother. It is nice to have the groom's mother and the bride's mother just enjoy the showers as guests.
Traditionally if the immediate family is invited to the wedding itself, but the reception is at a hall or a parent's home then guests should be invited then that is the only time you should invite others to a wedding shower. If the wedding is small with no other guests other than the immediate family then either the mother and father of the bride or the groom's parents could have a small reception at their home and those guests should then receive an invitation (can make the invitations online) or buy less traditional invitations at card shops and then invite certain relatives if you so choose. However, as long as other relatives and friends understand the reasoning for your wedding plans then you could get away with a wedding shower and wedding gifts and that is up to the bride and her mother.
Yes, it is appropriate for a bride to invite guests to her bridal shower but not the wedding which is being held in Vegas because the bride would realize that most guests may not be able to afford the trip to Vegas or they do not have the time. A shower gift would be appropriate and perhaps when the bride and groom get back from their wedding in Vegas they may have a small reception where the rest of their family and friends can attend once they are home from their honeymoon. Whether there is an event or not a wedding gift is etiquette in this particular scenario.
Not unless she's paying for the wedding - and even then it would be tacky. Only invite her close friends...and then pay for the wedding!
The bride should discuss with her biological mother how she would feel if her ex husband's common law wife was invited to the wedding. If the biological mother is comfortable with this then there is no reason not to invite the common law wife. If the biological mother is dating someone special or is remarried and bringing her mate to the wedding then you should ask your father and his common law wife without discussing it with your mother.
NO
everyone the bride and groom invite
The guests would stand when the bride enters the procession on her father's arm.
How to toast the mother of a bride
Sometimes. Other times, only those in the wedding party do. Check with the Bride's mother, she'll tell you which this one is.
A wedding toast to the bride's mother is sometimes made by the bride. She will thank her mother for all she has done for her.