There are of garden hose manifolds available in 2 or 4 outlet sizes at any big box store.
Stepping the outlet down to garden hose size/male thread is a job for pvc.
On the subject of gravity fed irrigation, I'm trying to implement some of that myself.
The Edible Acres youtube channel uses a solar powered bilge pump to move pond water uphill through garden hoses into a galvanized trough.
The over flow from that trough goes to another trough which in turn goes to another, or to two others, etc.
They use watering cans to water from those distributed points.
I am trialing a 55 gallon drum->1/2" garden hose-> 1/4" drip irrigation line-> diy ollas system, inspired by this distributed reservoir idea.
In the past I've tried low flow drip emitters with 5 gallon reservoirs, but they didn't last long enough between refills.