How many litter boxes do youhave?
Does he do this more when the in/out cat is in?
Has anything changed in the home such as a new pet added or one lost?
We have one litter box. The other male cat mostly eliminates outside but sometimes indoors.
There does not seem to be a correlation with the indoor/outdoor cat.
We got the third cat, the female, last spring 2009. My wife is pregnant and expecting in December/January so we have been setting up the third bedroom as a nursery. Unfortunately, we do not have space for more litter boxes with the new baby and my step-son in the second bedroom.
I would love to have more resources for the cats but with the new baby it is very tough.
This does sound difficult as the usual suggestion is one box per cat (and they can be next to each other) plus one extra box!
You may want to get the cat checked for health issues as sometimes cats stop using the box due to urinary tract infections or crystals. You can read about urinary issues here
http://www.marvistavet.com/html/feline_lower_urinary_tract_dis.html
You can try using Cat Attract litter which you can read about here
http://www.preciouscat.com/
and Feliway cat appeasing pheromone which you can read about here
http://catfaeries.com/feliway.html
Make sure to clean any sprayed spots with an enzyme based cleaner such as Nature's Miracle or Simple Solution as examples.
For the vomiting I find using a higher quality food can help. Grocery store food usually is about the lowest quality and you may find a food such as Feliway, Blue for Cats or others will work better for your pets.
The urinating could be either medical or a stress response - just the changes for the new baby room could be enough to stress the cat into marking.
If the above doesn't work talk to your vet about a med to help the cat be calmer such as Prozac.
Hope this helps you!
Cat Health, Behavior, Care Expert
30+ years cat owner, rescue, breeding, study of behavior & health care