I had 4 in 4 years and never needed a double pram so I say invest in a good carrier instead

As for beds, my ds was in a toddler bed at 22 months, dd1 was in one at 14 months, dd2 at 10 months and dd3 has slept with us mostly. She is nearly 11 months and starts the night in a toddler bed then comes into our bed.