Well, I am not a container guru; but there are many here who are great Meyer fans and will help you step by step.
What I do know is the Meyer is quite sensitive to being moved, light changes, re-potting, etc. They typically react by dropping most or all leaves, later replacing them with leaves better adapted to the new environment.
I would be optimistic and patient, if you can do both at the same time; it will probably begin to produce new leaves soon.

use a bamboo skewer/wooden dowel to check the soil's moisture. the trees are probably in shock due to the root pruning. so i would not mess with repotting again until late summer. if you're worried about overwatering, use Al's Gritty mix. or you can buy a small bag of perlite and mix it in about 1/3 perlite 2/3 potting mix. main thing right now is to just make sure you don't over water.

set them outside in full sun. do not fertilize. do not move them around. just let them sit there in one spot. keep an eye on the branches, if they start turning yellow then brown, prune them off. hopefully they'll stablilze and send out some new leaves in a few weeks.

Thanks all. I will certainly hold off on fertilizing, but unfortunately, we're getting freezing temps for the next couple of nights and I have to bring them in. They don't go far (from my back deck just inside the door), but more leaves definitely fall off as they get rattled around.

I'm also afraid the soil mixture is very heavy, and so I thought about mixing cedar shavings to lighten the mix. Should I try to do this without repotting the whole trees? Someone also told me to repot into plastic as they may not be getting enough moisture (I watered recently and the pots are still wet; and I noticed no visible improvement after watering).

Could the pots be too big??

Frustrated :(

But grateful - thank you!

I would not worry too much about what you did because I see nothing wrong. What I suspect however, is that your trees went into shock when you transplanted them. Give them time and they will produce new growth.

Please tell us what size pots you used and how big the root ball was in comparison. It's important to make sure you don't over pot in a mix like that.

How many roots did you trim away?

As for the mix, yes, it is too heavy and it doesn't take long before root rot sets in, especially after a re-pot, since the plant shuts down until it takes to its new environment as John points out, and the new mix.

Please, tell us, did you wash all the old mix out before introducing an entirely different mix? I mean, almost a bare root. Clean roots.

Full sun would be avoided for any of my newly repotted trees, until I know for sure the roots are functioning and keeping the leaves well hydrated, which in your case, it may be too late.

I would worry about them and correct anything that will further the demise of your trees, the mix being my priority and do it as soon as possible. It is obvious they are not happy about something.

Mike:-)

Well, shortly after the post, I realized I needed to take action, so I repotted both lemons right away.

They were originally put into 12 inch terracotta pots, but I reduced the size of one to a 10 inch terracotta pot (the second stayed in the 12 inch). When I trimmed in the original potting, it was less than an inch off the bottom.

I repotted with 1/3 part of cedar shavings (as recommended by Four Winds Growers) and gave them a GOOD SOAKING of water. The roots were quite dry, no root rot had set in, and they were very healthy. The roots looked the same as when they shipped 6 days prior.

The GOOD NEWS: the next day after repotting and heavy watering, a few of the buds opened up! They smell fantastic. I imagine the plant wouldn't open buds if it wasn't bouncing back? They've also bee in full sun since Sunday. There are still some yellow leaves, and I lost a few more (maybe 1 a day from each, rather than 6+ a day from each), but I take it they're recovering?

After seeing the buds open up, I gave a light feeding and another watering today. We're having night lows in the 50's, so I'm leaving them outside at night now too.

Are they on the mend?

Honeybee, Mike gave you good advice about keeping them out of direct sun, it may be a couple of weeks before the roots are fully functioning, and you'll want to re-introduce them into full sun gradually. Sounds like you found the problem ( soil was dry) and they are happier now! Careful not to go too far the other way with watering. If you have a spray bottle, the leaves might benefit from a spritz in the heat of day. This is just my opinion, but I would make sure the leaves had plenty of time to dry before facing night temps in the 50's.

Glad you found the problem! It always seems to be that we ourselves always do that because only we ourselves know more of teh details that we forget to post here.

All we can do is direct you into the right area, and help you put your thinking cap on. If you had said that leaves were falling off green that would of been easier.
Usually, leaves that fall off yellow are not due to under watering but over watering and or soggy soils, so I am very happy you figured it out.

MIke