You may have chosen to add the extra parent/sibling portion onto your session and have a few questions. This add on includes an extra 5 photos onto your total of images that you get to select. And boy I hope they are hard to choose because they are always so hard for me to narrow down! But lets talk about the details here for a minute.
Backgrounds: I use white, black, and grey as my backdrop options for parents with the extra option for a wooden backdrop for little sibling sessions.
Outfits: I have a limited number of dresses for little girls 1-4 and am working on more, but it's taking me some time. As for everyone else, I suggest wearing some sort of neutral whether that be whites, creams, golds or blues for boys like the photo above. To make your photos even more timeless I would suggest wearing solid colors with no logo of any kind. For parents I like to kind of match them to the background. So if you decide you want a black background i would wear black for both of you. I like your faces and baby to stand out the most. Most of all, Momma find something you feel good in. If it turns out it's not one of these colors, as long as it's a solid color, wear it!
Length I like to spend only 15 minutes doing this portion. Though it is important to capture, the attention span an older sibling has with his newest addition in a new environment with lots to look at doesn't seem to last long. After the sibling portion is over, please have someone who can take your older siblings while we finish the rest of your newborn session. It is too difficult to wrangle an older one at the same time as your session for your newest addition.
Helpful Hints for a sibling session: I usually have some sort of treat that I will offer you to use as a bribe for 1-3 year olds, but if they have a food allergy or you don't want me to use anything please let me know before hand and bring your own bribery. Being in a new place with new people always makes for a little bit more challenging of a session than you want it to be and any sort of reward helps ;)