Lots of things here...

Should you consider mooring at BEYC/Saba instead of Leverick?
Only if you can’t get a ball at Leverick. Plus those mooring balls have been largely out of use or not maintained since Irma. I’m not sure if anyone is actually even using them, though I’ve heard a couple forum members mention they’d done it. My personal experience in May 2019 was that the other boat in our group ended up grabbing a ball at Biras Creek near BEYC after my boat snagged the last FCFS at Leverick. Our friends said there were several other boats on balls near them and they had no issues. So, if I were there again and Leverick was full, I’d scoot over to Biras Creek and expect to find several usable balls. In that case, however, you may be a bit farther than you’d like to comfortably dinghy over to Leverick.

Are all of your Grub & Grog locations actual stops you’re intending to make? Or are they simply your notes on what your options are? If you intend to hit every location you list on each day you may be overloaded on a couple of those days in my opinion. Just make sure you leave time to relax and enjoy everything, take it all in! Don’t forget about the kids and giving them some time to have fun too.

I wouldn’t worry terribly about skipping Trellis and Oil Nut Bay, but if money isn’t a factor you could probably make a whole day out of ONB. They have their recently opened marina village that is free to visit I believe, but there is a fee to visit their resort and pool area. Check their website for info. It looks fantastic but many people shy away from the pricing. The marina village on its own hasn’t seemed to impress a few forum members that have been there since it opened, so unless you plan on paying to visit the resort and pool area I’d suggest passing on ONB altogether.

As for Marina Cay and Scrub Island, I’d recommend grabbing a ball at Marina Cay and splitting your time between there and a short dinghy ride over to Scrub Island. Marina Cay has a fantastic view from the hilltop, and the restaurant has good food and the best painkillers I found during our trip. But you really don’t need much more than a couple hours there at most. Scrub Island is awesome. The kids will love the pool and slide (lets be honest, me and my adult buddies loved the slide too haha!). There is also a beach and pool on the north side of Scrub but I didn’t get to see it last trip. I think a day split between Scrub and Marina Cay is definitely worth it. Not sure if there is any fee to use facilities at Scrub if you’re not on the dock that night, might want to verify. They do have a nice market for provisions along with hot showers and clean bathrooms, so that’s another nice thing to have mid-trip.

One other stop you might want to consider would be Diamond Cay, which has the B-Line bar and Foxy’s Taboo. That was actually one of our group’s favorite stops and we will definitely include next time. The bubbly pool is a 10-15 minute walk from Foxy’s Taboo, it is pretty neat if the tide is coming in. The kids would enjoy it surely.
Another stop the kids would enjoy is right across from Diamond Cay, at Sandy Cay. The small island is great for an hour or two stop. There are all kinds of rock formations on the south shore that people have made from washed up rocks on the shoreline. Our group each found their own rock and we made a pile of our own, adding to the hundreds of others left by previous visitors. Kinda neat and the kids would probably enjoy that too. Sandy Cay is also close to Cane Garden Bay and Great Harbour, JVD. Definitely recommend if you’ve got a couple hours to make the visit, but there are only a few mooring balls FYI.

All this is just my $.02. Hope your trip is great!