Go ahead and put them together, they'll adjust to each other really quickly.
My first 2 had very different schedules. Oldest was late up, late to bed. She just slept through her brother's early up, and we did a lot of her going to bed routine not in the room where he was sleeping. When we had our 3rd, we moved daughter to her own room and put boys together at about a year, and the youngest just matched himself to brother's early schedule.
Kids are very resiliant and flexible. You'll have a week or two of adjustment, I predict, and probably grumpy-tireds during that time. But then they'll start adjusting schedules and getting used to sleeping through the other being there awake (make sure you don't leave them alone awake too long, depending on older's age especially). I think it'll be easier for them to adjust now than in a year or two.