looking for answers for my birds deaths

Hi, I have a question about my pet budgies. Sadly, I lost 2 of my 4 budgies in the last week. I think they were unrelated incidences, but I'm not sure. I have a couple questions that will hopefully provide me some closure, since I am lost about what happened.

Jay was my 5 year old budgie. A year ago he developed a tumor close to his vent that the vet said they could do nothing about. Jay lived with the tumor for a year, and nothing stopped him. He still ate, played, flew, bathed, he was a happy bird. Last week I came home from work and found him dead on the bottom of the cage. There was no sign of trauma - no cuts, bleeding, etc. He was acting perfectly normal before I left for work - he had breakfast and a bath that morning and singing and playing as usual. My assumption is that maybe the tumor was pressing on an organ inside his body and that's what killed him? But if you have any professional opinions I would greatly appreciate it.

Diablo was my 2 year old budgie. Very healthy, diet of seed, fruit, veggies and egg whites. very active. Last week as I was laying in bed in the morning I heard thrashing in the cage. I jumped out of bed and found Diable hanging on the side of the cage, looking panicked. I took him out of the cage and held him for a little bit. When he decided he wanted to go back to his cage he took off flying, but ran into the walls and ceiling. Very uncoordinated. I put him back on his perch and he seemed tired but fine. I took my fiance to work and when I came home just 90 minutes later I found him on the floor of the cage laying on his side. It was like he was paralyzed. His legs were stiff and he couldn't sit up. I held him in my hand for a little bit and then he passed away in my hand. The only thing I can think of is he had a seizure (if it was a stroke wouldn't it have affected only one side of his body?) but if he did indeed have a seizure what is it that would have killed him? What made his poor body slowly become paralyzed?

My final question is that, I feed the pigeons outside on my balcony. I go outside every day to fill up the feeders. I'm good about cleaning up out there every few days, but I won't lie, there is pigeon poop and seed husks out there pretty much all the time. My fiance is convinced that the "fumes" of the pigeon poop caused my birds deaths. I think that's highly unlikely. Am I putting anyone (such as us humans, or my 2 remaining budgies) at risk by the pigeons hanging around outside?

Thank you so much for reading, it's very much appreciated!
Erin