The main problem with citrus is overwatering and not using the corect fertiliser (needs micronutrients) ,
use a compost made up of something like 70 percet perlite and 30% ericaceous compost (make sure its not one with added water retaining crystals), a better compost mix is 70 percent CHC (coconut husk) and 30% the same ericacieous compost
If using CHC you need to presoak it in water for a few days, with a few spoons of epsom salts and calcium nitrate ( to act as exchange ions to remove salts in the CHC)
You can get citrus compost, but still they tend not to drain quickly enough, so its best to add some perlite or bark chippings
You need to let it dry out to very dry, dust dry on the surface and dry till about 3 inch deep, then soak the pot totaly , never give a bit of water here and there , the roots will rot
Use a fertiliser made for citrus, best with a summer and winter fertiliser, the different formulaton gives a boost for fruit development and holding , and leaf growth at the correct times, every now and then spray with epsom salts to boost magnesium levels
If the compost needs to be more acid, use sulphur powder, it works slowly, but works well
dont over pot them, its harder to water them and you get less fruit for some time as it grows roots and branches
Its the overwintering that gets difficult!,
If its light, the roots need to be over 70F, with humidity of something like 60%+
If the roots are cold, with light the leaves all fall off, then it needs to be left dry, if roots are wet with no loaves the roots will rot
But if theres fruit on it you still need to water and feed occasionaly in the winter
You do need to keep them inside in the winter if small, but in the summer there best outside,
I have a few large trees outside, even now in the snow there outside.... too large to move in the house! (280 litre pots, 12 foot high), wrapped in frost cloth with Christmas lights to keep them a bit warmer
Mandarin tree
Lisbon lemon tree
My trees inside the house are on heater mats to keep the compost at 88F with metal halide growlights, to keep them growing for now instead of going dormant, in january i will let them go cold to get required chill hours to flower next year