Before I send your question along to a fruit tree expert, could you attach 2 more pictures—

1-one far enough back to show the whole tree, top to soil line.

2-A second showing the branch tip and about 2 feet long.

To add pictures, click the link in your email and go into your question on the website. Click the “Drop files here or choose them” them” below the response box to attach them. You can upload .jpg, .png, .gif, .txt, or .pdf. NOTE- each picture must be 8mb or less.

Include any history you can, how old the trees are, has any digging been done in the root area, how often they are watered and fertilized.

Is the tree located at the top or at the bottom of a hill, or a flat area?

What fungicides or other pest treatments have been applied and how often?

This detailed information will help our fruit tree expert assist you. I will watch for your additional info- thank you

Thank you, Audrey, for the additional information.

The spots on leaves could be frogeye leaf spot. It is always associated with cankers on the limbs. Any dead or dying limbs should be pruned out. To confirm that it is frogeye, please submit samples to MSU Plant Diagnostic lab( instructions, sample form, and fee schedule is on their website)
https://www.canr.msu.edu/pestid/
Frogeye leaf spots- https://ohioline.osu.edu/factsheet/plpath-fru-07

You may consult a certified arborist instead of using the lab. Find certified arborists here
www.treesaregood.org

Crabapples are Malus species, just as are apples. They are all susceptible to the same diseases and pests. Some species are more resistant than others. There are several fungi that cause leaf spots, apple scab being the most common and is usually the one responsible for causing early leaf loss. 
Following a regular spray schedule can prevent leaf spot diseases, but once fungi are on the leaf buds in early spring, there is no curative spray.
Your tree is large, has some dead limbs, and you stated it lost its leaves early. Having the tree assessed by a certified arborist is probably best, since he/ she will come on site, diagnose the leaf spots, and give you a complete care plan for pruning and spray schedule.

Pruning and thinning the crown will also help air circulation, which helps leaves dry more quickly, and so some fungal issues are reduced. 
See the spray schedule here, although powerful equipment is needed to spray a tree of this size properly. http://hyg.ipm.illinois.edu/pastpest/200801d.html


Failure to flower on crabapple can be due to unusually severe winter temperatures, a spring killing frost or freeze, application of too much nitrogen fertilizer in the tree’s root zone, less than full sun.

Flower buds are more temperature sensitive than leaf buds. If buds begin to swell and then are hit with freezing weather, they can be so damaged as to not open.
If the tree is sited in a low spot in the landscape, cold air sinks at that spot, so a colder micro-climate there can freeze buds when plants on flat or elevated areas are not. 
 Apple trees want full sun, greater than 8 hours per day. As trees around this crabapple grow and shade the tree for more hours in the day, the tree will flower less.

You may check your area’s past temperatures with the Enviroweather tool, setting it to a station near you.
https://enviroweather.msu.edu/weathermodels/weathersummary

Since your neighbor’s tree also failed to flower, I suspect a late freeze affected the flower buds.