Roundworms ahhh help please

So I took in a stray cat in December, it’s about a year and a half old about a week and a half ago he vomited up 2 live roundworms so I dewormed him and nothing happened no worms came out in stool no more vomiting ....until today when 3 dead worms came out when he vomited up a hairball and some food is this normal? Should I be seeing dead worms in his stool ? Should he still be throwing up dead worms ? The next treatment I’m suppose to give him on the 11th ...is he still contagious ? Are my other 2 cats at risk if they use separate literboxes and food bowls? I’m seriously grossed out and need some advice and info TIA for any help.....

Re: Roundworms ahhh help please

Ugh no experience but that sounds nasty!
Does he still go outside?
I would call your vet and ask for advice.