This is why I always have the electrician run the supply wires in the ceiling, with plenty of slack. We wait until after the drywall is done to cut the holes and use remodel boxes. People can’t visualize. Even when you draw them diagrams. Or, do an actual real completed DESIGN from the beginning, with all choices measured and specified, and SET. Instead of winging it without the ability to visualize. Design BEFORE you do any demolition or building anything. Then the boxes and lights go where they need to go with no angst.

As a general rule, odd number multiples work best. But that all depends on the size of the island and the size of the fixtures. If you want those fixtures pictured above, get two. If you want (3) fixtures, go smaller, i.e. no larger than 8" in diameter.

I'd think if it were centered it may look ok, but then light distribution may be funky unless you have more overhead lights you plan on using it might work.

Some photos are attached. Island top is 108" x 54", waterfall top, honed black pearl granite. White cabinets. Ceilings flat 9'. Kitchen is open on 2 sides. Need advice on size of pendants if using two oversize pendants. I'm thinking width somewhere in 24" - 36" range depending on height, shape etc... I don't want them to look too big nor too small. I can use 3 pendants also, not set on 2 or 3, not sure. There are photos below of the type of pendants I'm leaning toward as of today but I'm open. The backsplash and hood behind it will be a pretty bold porcelain and I don't want to distract from that either (photos below).