See top right of page, under CANE GROWERS. (Never mind the New England part, mock oranges (Philadelphus) are pruned the same everywhere).

http://www.plantamnesty.org/assets/docs/guide-newengland-2013.pdf

With that foliage color these must be P. coronarius 'Aureus'.

i would prune the largest 1/3 of the stalks AFTER flowering ... down around 3 to 6 inches from the ground ...

the other term to google is REJUVENATION PRUNING .. hit the video button ...

ken

https://duckduckgo.com/?q=rejuvenation+pruning+philadelphus&t=ffcm&ia=web

Here is my neighbor's mockorange. This is the kind of old-fashioned shrub that needs plenty of space. My neighbor does nothing to this plant as far as pruning. The reason it is think, full and loaded with flowers is because it is in the full sun.

My suggestion to you would be to move your MO to a place where they can reach their full potential with full sun and plenty of space to develop.

If these are 'Aureus' partial shade would probably be preferable. Otherwise there might be some burning in summer.

BTW this shrub smells heavenly!