1-I have had four cats but they all died.
Could one use this even if one had the cats at the same time?
B) Are 2 and 3 correct?
2-I have had four cats. Three of them died. I still have one.
3-I have had four cats but three died and I have only one now.
4-I had four cats but three of them died.
Could one use this sentence if one didn't have the cats at the same time?
1- The past would be more likely.
2- I'd say say three 'have died'