My cats tackle and hiss. Are they playing or truly fighting?

It is OK behavior but not great. I am worried that this could escalate into a serious fight. I suggest you try using some Feliway diffusers in the house and do some environmental enrichment for them. Those two things should help. ( https://www.feliway.com/us/Products/FELIWAY-MultiCat-Diffuser ) ( thedrakecenter.com/materials/environmental-enrichment-indoor-cats ) ( https://www.youtube.com/watch?v=AejmrLa_Cs4 )

I recommend you put some Feliway diffusers in your house and do some environmental enrichment for the cats. Usually these two things help. ( https://www.feliway.com/us/Products/FELIWAY-MultiCat-Diffuser ) ( thedrakecenter.com/materials/environmental-enrichment-indoor-cats ) ( https://www.youtube.com/watch?v=AejmrLa_Cs4 )

This sounds like a typical play behavior. In general watch for signs that one cat is trying to avoid the other cat. Watch for the cats hissing at each other. Watch for any signs of intentional bites or scratches that leave marks. If the cats are willingly interacting and you don’t notice any hiding or avoidance behaviors, this is likely consensual play. You may also look into reading a few books about cat behavior as it is not only informative but also fun! I hope this helps.

No, it doesn't like like fighting to me. They are likely wresting and playing with each other. If there is no hissing and screaming, they are just having fun with each other. If there was fighting, there would be vocalization, hissing, and tense body posture. If you aren't seeing any of that, you don't need to separate them when you are at work.

It sounds like you have a behavioral issue in the house. One of the cats is trying to be dominate over the other. I would make sure you have 1 more litter box than cat. Also have multiple areas to place food and water. This will eliminate competition over those things. I would try feliway in the rooms the cats spend the most time. This is a pheromone to help with stress. Increase exercise as best you can. They do make toys you can hid treats an the cat has to get them out. Also hid toys around the house at night so Mo and Francis have something to do. IF that does not work it is always best to have a good exam by a vet to make sure the aggression is not due to illness or pain. thanks for using pet coach

If your cats have spent most of their time outdoors and now are spending time inside together then this change in environment could be causing tensions. If they are still outside all the time then it is possible that a new cat has come into the neighborhood and this has disrupted the social structure of the cats, or potentially one of the cats could be feeling unwell and therefore being more defensive, or they could feel they are having to compete for food/shelter. I would be sure both cats have equal access to food and water (they may need their own separate areas to eat/drink so they don't feel threatened) and litter boxes indoors. When indoors I would recommend the use of the Feliway Multicat diffuser https://www.amazon.com/CEVA-Animal-Health-D89410B-MultiCat/dp/B01AVHPFDS/ref=sr_1_4?ie=UTF8&qid=1503838561&sr=8-4&keywords=feliway+multicat, which is a pheremone product. I would consider an examination by your vet to look for underlying health problems as well.

My guess is that you did not do a gradual introduction with them?? If not, you may have to go back and revert to doing that along with these other recommendations. ( https://www.americanhumane.org/fact-sheet/introducing-cats-to-cats/ ) I recommend you put some Feliway diffusers (Multicat) in your house and do some environmental enrichment for them. Usually these two things help. ( https://www.feliway.com/us/Products/FELIWAY-MultiCat-Diffuser ) ( https://www.feliway.com/us/Why-Use-Feliway/how-to-stop-cats-fighting ) ( thedrakecenter.com/materials/environmental-enrichment-indoor-cats ) Hope this helps. If you have more questions you can always opt for a private consultation where we can chat back and forth. That way you can ask as many questions as you'd like. Best wishes.