That looks like pear trellis rust. There are two main rust diseases of pears in Oregon, Pacific Coast Pear Rust (Gymnosporangium ibocedri) and Trellis Pear Rust (G. sabinae). Rust fungi typically have two different hosts, the primary host (ex. your pear tree) that will display severe symptoms and a secondary host (ex. a juniper tree) which may only display minor symptoms and effects. Trellis Rust causes acorn shaped aecia on the lower leaf surfaces later in the season. Based on what I can see in the photos, this looks like Trellis Rust: https://pnwhandbooks.org/plantdisease/host-disease/pear-pyrus-spp-trellis-rust-european-pear-rust.

The best control is to remove the alternate host that is within a 1,000-foot radius of the tree (for trellis rust, this means all juniper), however, in urban environments this may not be an option if the hosts are in neighboring yards. There are no chemicals registered for home use for either species of rust, so your best option is to hire a company that is licensed to apply a commercial pesticide (see: https://solvepestproblems.oregonstate.edu/index.php/pesticide-information/hire-pest-control-company).

Pear rust can affect both European and Asian varieties of pear. Bartlett is considered less susceptible to Pacific Coast Pear Rust, but it can be severely affected some years. There are no listed resistant varieties for Trellis Rust. Other management practices include removing and destroying infected leaves, stems and fruit to limit the spread, collecting and destroying fallen fruit beneath trees, and of course removing alternate hosts when practical.

With regards to the small fruit, there are a number of factors that could cause the tree to produce smaller fruit. Lack of water during dry spells or heat waves can impact fruit development. A freeze event during bloom can also affect fruit production and size. Do you prune and thin the trees? Do you fertilize the trees? Pruning, thinning, and fertilization, or lack thereof, all impact fruit size as well. Be sure to prune the tree during the dormant season, apply a balanced fertilizer next spring, and be sure the tree is getting enough water during the summer months, and hopefully you will see better fruit set next year.