Congratulations! I have No experience with feeding twins, but I heard if you can get them into a rhythm and routine your older baby may even help with supply... Eg: Older one to start the feed to prevent spraying/leaking, followed by tandem feed. Or for low milk supply, tandem feed twins then older one to suckle and help milk production. Or you can do a 3 way cycle. By this time your older one will mainly be in it for the cuddle time!
I think that if you get your supply in good balance then you can "relax" and let the babies sort it out. Good luck! I hope you find it works for you!