Where are you located and what sort of hydrangeas are they? Have they bloomed in the past?

Any chance of photos?

yes I can take photos. They have been pretty heavy/reliable bloomers. I’ve struggled with them to figure which type they are. this is the first year all 3 have been devoid of flowers with NO hint of buds! I’m in Northern NJ. The first and last pix are of the one I want to split. I was relieved to find out yesterday there is a division between 2 sections of the plant.

Most likely Hydrangea macrophylla. You can "downsize" now if you must but you will be effectively cutting off next year's flower buds (which are latent and already present in late August). And the shrub will grow back to the same size next season.

Dividing or splitting a woody plant is not always successful so do so with care.

Sounds like you had a bad autumn 2024 through spring 2025. Looking at the records, Northern NJ experienced a record dry autumn 2024, the third driest January in 131 years plus an exceptionally dry December 2024-April 2025 precipitation period, all of which likely stressed hydrangeas heading into dormancy. Drought during this period could have weakened the buds, making them unusually vulnerable to your normal late frosts.

Aim to keep the soil evenly moist always but especially when it is so dry. Consider testing the soil at a depth of 4 inches very frequently when dry or hot so you can immediately irrigate when the soil feels dry at that depth. Also, maintain the soil mulched with 3 to 4 inches of organic mulch to minimize soil moisture loss and protect the roots from hot-cold temperature extremes. Once summer temperatures recede, reduce watering to the equivalent of ‘spring watering levels’ once temps are sustained at or below 85F. Then once the shrubs go dormant, reduce watering to dormancy watering levels as there are no leaves requiring water. Finally, stop watering once sustained freezing temperatures arrive.

Normally, ensure you do not use high nitrogen fertilizer or prune leafless stems prematurely when they have dormant flower buds in the leaf axils from late summer to spring. You can interpret the color changing phase of the blooms as a signal to be wary of pruning going forward from then thru spring.

The 5x5 dimensions do not sound large for this type of hydrangeas but if you determine that you do need to control the size now, do so but expect diminished/no blooms in 2026 if the stem endings already have buds in the leaf axils. To minimize a complete loss of flower buds, perhaps consider doing rejuvenation pruning in winter instead. Consider doing the shrub division after the shrubs have gone fully dormant.