Hmm... I think there are a couple of layers to this one... Please bear with me because this is a longer explanation.
Do I have all the facts correct?
The trees themselves are 2-3 years old, but you have only had them for about 5 weeks. And they came potted. (I checked and it looks like the grapefruit do, but I got mine bare root from them.) And you repotted them in new soil that is NOT amended but is citrus soil.
When you repot a citrus tree it will typically take at least 4-5 months for the tree to settle in well, during that adjustment period I expect to see a certain amount of leaf yellowing and fruit drop due to stress. Moving to the new climate of your house will probably slow that down too. (Not to mention the shipping stress.) After that, the tree will begin to grow properly again. If the soil was amended it usually takes about a year for the fertilizer in the soil to be used up.
Watering problems usually show up pretty suddenly when the leaves simply fall completely off. Yours have not and "watering deeply" sounds good, so I am going to assume that part is fine.
It is very, very hard to kill a citrus with under-fertilizing and it takes a very long time. The leaves slowly pale, become blotchy, reduce in size and the growth stalls.
Romeo's fertilizer is very strong, at the listed indoor/potted plant concentration I would expect the trees to be in full fruit and very heavy growth. Yours are not. At two to three years old they are just old enough that they MIGHT crop and are still in their adjustment period. I do not think they can currently handle the fertilizer strength.
And truthfully, I always tend to under fertilize. I have discovered that it does not effect the ability of my plants to crop well, but does cut down on some of the bug problems because the trees do not flush out with so much green juicy growth every chance they get. (Mine are in a greenhouse, so I have to watch everything very carefully for developing bug problems because they spiral out of control quickly.)
I would advise simply not fertilizing for a couple of months and watching your plants carefully. If they start to look worse, bring more pictures and we can work it out. There are many citrus experts on this site! If they start to look better, you can slowly add in fertilizer in about 3 months. (Start with one dose at 1/4 strength, and then wait. It only takes about a week for citrus to show the effects of feeding.)
I hope this is a better explanation. (If not, ask me more questions and I will try again!)