diannelmt:

alderman plum was brought out by the University of Minnesota. Jap x american plum hybrid. It does need to
be cross pollinated. Toka is the universal pollinator for
all the Jap x american plum crosses.

Bartlett pear can produce some fruit if not cross pollinated but not many. Pears require cross-pollination.

Peaches are self-pollinating.

MOST peaches are self-pollinating. Self-pollinating properties of Bartlett may vary with climate, apparently. Many recommend planting Japanese/American hybrid plums very close to pollenizer varieties. Some people recommend 100% wild American plums (See discussion in Fedco catalog). Toka is frequently recommended as a pollenizer, too.

If you are out of room check with your neighbors to see if they have fruit trees or want a cross pollinator to match your trees.

Also Dave williams nursery I think has a video of planting more than one tree in the same hole.

Don't give up.

Okay, I called the nursery and I'm hoping to modify my order (they have to call me back).

I'm adding an Asian Pear to the order as well as a Stanley Prune Plum.

They told me that these will help cross polinate the trees I ordered.

I hope they are right! I have just enough room for two more trees!

Stanley is a european plum and Alderman is an asian. They have different numbers of chromosomes so no cross pollination at all. No big deal graft another asian plum into the Alderman next season.

The Asian pear may bloom before Bartlett, too. Is it supposed to be a self-pollenizing variety? If so, you might want to cut a few branches when blooms are at the "popcorn" stage and refrigerate them (in a vase with water, lightly covered as with a plastic grocery bad) until your Bartlett blooms. Or you may need to graft in another Asian pear and/or another European pear if bloom times are too different where you live.

But this is a different problem than the incompatibility of Alderman and Stanley discussed above. The pears you ordered should cross-pollinate if they bloom at the same time.

I'm hoping that the customer service rep knew what she was talking about when we modified the order.

She had additional info in front of her that was not on the website and seemed confident that we chose appropriate pollinators. I'm keeping my fingers crossed.

Uh oh, they weren't able to modify my order. The original trees have shipped.

I also ordered two apple trees which bloom at different times... an Arkansas black apple and a yellow delicious. So I'll need something to pollinate both of them, as well as the bartlett pear and the alderman plum.

I'm thinking of shopping locally since I can't add these new trees to my existing order and take advantage of the free shipping.

I appreciate the advice, any further suggestions are greatly appreciated... and BTW, I need dwarf trees.

I do have crabapples on my property and possibly an ornamental plum, will they help at all? I'm on 14 acres in the country so I have no idea what the neighbors have or what might be growing in the woods either.

AB and YD bloom periods may overlap sufficiently, and if you have ornamental crabs on the property, there'll probably be plenty of pollen (provided you have pollenators - bees, etc., present) to get the job done.
As carolync1 indicated, you could even develop some grafting skills and graft additional varieties into your Bartlett to provide cross-pollenization sources down the road, if you're limited for dedicated 'orchard' space on your 14 acres.

Well, turns out I was able to modify my order after all. I exchanged the Arkansas black apple with an Empire so it will be compatible with my yellow delicious.

My concern now is with the plums. I guess that the Stanley prune plum and the Alderman won't pollinate each other?

I think Spartan-apple and AceofSpades were right: you should consider getting (or grafting in) a Japanese/American hardy hybrid (like Toka) or a native American plum (you can keep it small through pruning) to pollenize your Alderman. Consider planting your pollenizer close to your Alderman. As far as I know, Stanley is self-pollenizing.

I think that's what I'll do. I'll graft something to the Alderman.

It would be great if the Stanley was self pollenizing!