Potting more than one Christmas Cactus in the same pot

I have quite a HUGE collection of these plants. Unfortunately ive had two issue's. The first is that I have medical issues. Can be quite debilitating at times so they tend to get neglected. I've started today using a calendar on my phone to remind me to water. However I have so many in pots and they are tightly close together on several plant stands including my kitchen counter. My first issue I noticed is that I was dropping branches off them. Still in pretty good condition. I have no clue what the color was so I started a pot to put random one's in. Glad to know you can mix the plants. I was afraid of possible crossbreeding. I'm assuming foliag dropping is b/c of lack of water??? My second issue is that I love succulents/ cacti. They have shared my counter space. I believe one of the succulents i purchased had spider mites??? Looks like lil white cotton. It unfortunately killed most of my succulents and it is now on my Christmas Cactus. I used 1:1 ratio alcohol/water on remaining succulents and just used a spray bottle and it worked. Is this safe for my Christmas Cactus's? Of course I isolated the infected ones. I tested a leaf w/ mixture and it seemed to tolerate but my fear is that it may be in the soil. These particular cactus have hard soil. I bought from a nursery on eBay and that's how it arrived. Even though it's been almost 2 years after watering more often they never get completely moist. Almost like cement. I've had to initially water them by holding them in a tub of water just so water could be absorbed. In saying that and believing the mites have managed to get in the soil. How do I treat these and kill the mites? Unfortunately, I did have a real Christmas Cactus that has bn infected & not sure it is salvageable. It waspassed down from generation to generation. We researched and it stops in the late late 1800's. I will try anything to save this particular heirloom Cactus....HELP PLEASE...Also just another side note I have a mother plant I use for cuttings from time to time. My elderly neighbor gave it to me and she received it from her grandmother in 1982. She knows it is older than that b/c it had bn passed down previously from at least 3 generations of grandmother's. So I definitely know these plants if taken care of have a very longevity life span. Sorry to be so long but wanted to share a few things an also ask how to treat my infestation :( I know I can repot & water the roots but the one's from the nursery are hard as a rock after over a 2yrs of watering. I might add they have still bloomed. Any help or advice greatly appreciated, ty!!!!

Alewis1095.. Thanks for sharing your history, experience, thoughts and issues concerning these plants. I wished I had a green thumb so I could advise you a lot better. As far as that cement like dirt... "I would change it and use a cactus mix.

I personally like to use Scott's potting mix and I shy away from potting mixtures that hold water for fear that it will rot my plants.

I have used the soap and water method in the past and have also used Neem oil.

I found a link that I hope will be useful.

http://www.guide-to-houseplants.com/neem-oil-insecticide.html