The plants appear to be sort-of ok.
The red color in the foliage indicates that they experienced some form of late frost though. Leaf surfaces damaged by cold temps will likely turn brown and sometimes disintegrate on their own. The "worst" one of the three plants is starting to put new growth from the base. All of this indicates that the roots are in good shape.
The partial lack of foliage in the "worst" one is also normal in Spring and it suggests that temperatures were cold enough to zap the foliage of stems and-or even zap the stems themselves. If the dead looking stems fail to leaf out by the end of May, you can very lightly do a scratch test on the stems to see if you see green or not. If not, prune the stem to the ground. There is new growth coming up from the crown so that means that the roots are ok and you will have new stems. Maybe those dead looking stems will develop new leaves in 2-4 weeks.
Maintain the soil as evenly moist as you can and mulch them. Slowly transition the plants to more and more sunlight until they are planted in the ground. They typically need morning sun only (shade in the afternoons and in the evenings), dappled sun or full -but bright- shade.
When to water: insert a finger into the soil to a depth of 4" and water of the soil feels dry or almost dry.
How much to water: varies depending on soil types, etc but start with 1 gallon per plant and see if, sometime after watering, the soil feels moist down to a depth of 8". If the soil is not moist at a depth of 8" then increase the amount of water per watering. Typically, start using around 1 gallon as soon as they leaf out in Spring (more if it does not get moist down 8" deep). Then as temperatures remain above 85F most days, increase the amount of water. Then as temperatures remain above 95F most days, increase the amount of water further. Always water the soil and never water the leaves. Water early in the morning, in all directions around where the root ball is located (where all the stems are coming out of since there are no roots much further away yet). As temperatures moderate in the Fall, reverse this process. Reduce the amount of water one notch when temperatures regularly stay below 95F. Then reduce again when they stay regularly below 85F. Tweak as needed for your conditions which may require even much, much more water than those numbers. Once the plants go dormant in the Fall and the leaves brown out, you can reduce watering down to once a week or once every two weeks, depending on local rains. If winter is dry and the soil has not frozen, water like that. Resume normal Spring watering frequencies and levels once you see leaf out.
How to set a sprinkler in Spring: use the finger method mentioned earlier daily, in the early morning 6-8am, for 2-3 weeks. Water 1 gallon when the soil feels dry or almost dry. If you water, make a note in a calendar saying that you watered 1g on day xyz. After 2-3 weeks, review the notes. Average out how often you were having to water (once every 3/4/etc days for example). Then set the sprinkler or drip irrigation (or manually) to water 1 gallon of water on that frequency of days (every 3/4/etc days). If weather conditions change and temps go up/down by 10 degrees or more, use the finger method for 2-3 weeks again to see if you need to tweak things.
Did you give them enough water: remember that a single watering should reach around 8" down.
Note: if your soil is sandy, you need more gallons of water than normal, usually 50% more, and the soil needs to be mixed with 50% organic compost as sandy soil is low in and lacks some minerals. An annual layer of organic compost helps sandy soil as well as more fert applications.
If the pots already contain those round fertilizer pellets, they will not need to be fertilized now. Hydrangeas are not heavy feeders but during their first 3 years or so, I would give them 1/2 to 1 cup of cottonseed meal, organic compost or composted manure. You can also use a general purpose, slow release fertilizer that has a NPK Ratio of around 10-10-10.
To help them on windy days and hot/cold days, maintain 2-4" of organic mulch (no rocks though) year around. After they are established, they can feed off the decomposing mulch if your soil has no issues.
For the one without almost any leaves, I would just mulch and maintain the soil as evenly moist as you can. No periods of moist soil followed by dry soil, followed by wet soil, followed by dry soil, etc. This type of inconsistent watering can make it hard to bounce back. Do not fertilize it now. If it does not have fertilizer pellets then just wait until it recovers a little more, starts to leaf out, and the leaves are larger. Then you can fertilize it (if temps are not summer high by then). The last fertilizer application for hydrangeas in the ground should be at least three months before your average date of first frost (that occurs close to the middle of Dec for San Jose)..