Wow their birthdays are gonna be close
If you prepare the eldest properly you should not have any issues. I let Brandon help me get Liam's room ready eg where do you think the cot should go, here or here, I pre-chose a few colours for the paint and let Brandon decide which he liked for his brothers room, let him feel Liam kicking in my tummy, took him along to gynea visits so he could hear Liam's heart beat and see him in the scan, if I bought nappies, I asked which brand he prefered, ditto on the scents of the wet wipes etc
All of that made him really excited to meet his baby brother and when they did meet I cried cos he was so spell bound - I even found him sleeping on the floor next to Liam's cot one night. When asked why "So Liam not scared"
Preparing your child for anything from a visit to the dentist to meeting a sibling to starting school is the most important way of avoiding unwanted suprises. Most children don't deal very well with the unexpected