These are not mealybugs. Cottony cushion scale is very difficult to control...and can lead to the demise of citrus if left unchecked. Your good image shows a number of female scales carrying full egg sacs around with them. Each sac holds many hundreds of bright red eggs. Tear open one and take a look for yourself. After the eggs hatch, the 'crawlers '(hatchlings) take off and go exploring....as a matter of fact, this particular scale stays mobile. Early instar stages look entirely different from their highly recognizable egg parents, which makes their control even more difficult. Hand wiping with alcohol a nearly futile option. I believe I see one of the earlier nymphs in the picture...at 3:00 o'clock just to the right of the adults. The younger crawlers are much too small to observe easily. You should do a bit of research that you know what cottony cushion scale insects look like in all stages. Also important is recognizing the beneficial critters that usually do a great job of control for us. A species of ladybug, the Vedalia beetle is the most important predator of these pests. There are no good chemical controls. This post was edited by rhizo_1 on Tue, Mar 19, 13 at 18:18

How much sun and what indoor temps has your tree been exposed to? It is a common problem for potted citrus to loose leaves when moved indoors. The usual problem is the tree top continues to get sun but the root temps are too low to bring in water, so the leaves end up dropping. This can be a big problem for folks who keep the pot below the window level and tree up in the sun. IIRC the temp at which the roots stop working is ~55F, which is easy to get to if your plant is right next to a window in the winter. There is quite a bit written out there on the web about this. Basically you need to get the roots and top in balance. Either less light to the top and/or warmer roots.

The soil looks like you have a lot of clay. When we plant fruit or citrus we never add fert. The tree will go into shock and it needs to get some what established before adding fert. But now that you have what kind did you add? Because of the clay soil(?) hopefully you dug a hole a lot bigger than the root ball. Also you really need to dig a molt around the tree out to the drip line. Fill that with water and see how long it takes to drain. If it drains quickly then great, if it doesn't then the clay is maybe causing a problem. All our trees have a moat and as they get bigger the moat gets bigger. Hope the tree is a dwarf because if its not the roots will eventually destroy that slab and maybe even the tree. Trees need room. Carlsbad Ca Hope this helps PS If its clay and the soil has not been amended your tree will end up in its own personal clay pot.

Lot of questions, I'll try and give my opinion. I'm not an expert but am a long time gardener. However, many others here have more experience keeping citrus trees inside. My winter is not that cold, so mine stay outside. So my advice on keeping them inside is limited. Check out the threads on keeping them inside during winter; there are a lot of them. There could be several reasons why your lemon has few leaves. As the ones left look good, I'll rule out lack of nutrients. You don't say what soil mix the lemon is in, but in general if the soil does not drain fully, and/or is compacted from too much organic matter like peat moss, the lower half of the pot could stay too wet for too long even though the top part feels dry. Most common reason for leaf lose in potted citrus. The lemons look ready to harvest, I'd go ahead and start using them asap. You tree will not grow more as long as the fruit is still hanging on. Probably best to re-pot in spring and just try to get it through winter inside for now. Get a long thin wooden dowel and check the water level down to the bottom of the pot before watering every time for now. It is a good idea to supplement lighting inside for winter. There are few good threads on the forum now about inside lighting. Check them out. The grapefruit does look good. You may lose some leaves on the citrus trees, due to lower light levels and changes in temperature from outside. It may or may not affect the fruit, time will tell. Don't spray anything unless you see an issue like scale, etc. Just examine them couple times a week to check for the beginning of a problem. You shouldn't need to cover them inside, if it's warm enough for you it's warm enough for the trees. If you turn off you heat at night that could be a problem. Try and keep nighttime temps no lower than 50*f. The peach can be trimmed anytime between now and early spring. It should get a spray of fungicide when it goes back outside for peach-leaf curl. Copper based sprays work best for that, look for it at your local garden center. Pre-mixed ready to use ones are available and are the are easiest. Citrus trees don't need it. It's safe to trim peaches by 1/3 off the ends of the branches. Also cut out broken and crossing branches. By the way, unless you live in really northern cold areas like upstate New York or Canada, the peach could probably stay outside. They're winter hardy in USDA Zones 5 to 8. You can trim your tangerine (really mandarin) when it is at the height you want to keep it at. Citrus can be made more bushy by a method called tip-pinching. Basically you cut off the tip of each branch down no more than 3'-7" depending on how long it is and how short you want it. The tree should then send out new branches lower down on the branches and trunk in spring. Wait until spring to do this. You will have a smaller crop that year as the tips are where you get fruit, but the next year the tree will have even more. Do search the previous threads on the forum, lot's of good info there that will answer your questions in greater depth. Especially how to get them through winter. Good luck.