Re: What do you think???
I take in strange cats all the time. Every single one of our cats (a dozen at the most and currently eight, right now) was rescued from one dire circumstance or another. I also foster kittens and cats, some who arrive feral and need to be tamed and socialized before they can be adopted through the program. The only precautions I take are keeping the new cats isolated from my permanant cats. If any cat has an obvious respiratory infection (coughing, sneezing and mucus crusted around the eyes, nose and mouth) I keep them isolated with TWO doors closed between them and my housecats, wash my hands and sometimes change clothing after handling the sick cat.
After the new cat(s) have been given a clean health-check and their first vaccinations, I will allow mingling with my own cats. My indoor cats do not get vaccinated every year, though my outdoor barn cats DO. This works out for me, my situation and the area of the country I live in. If I were in an area that had a high rate of diseases for cats, I would be much more vigilent in both housing (no access outdoors) and vaccinations.
I would also like to suggest, if you take in one kitten...could you take all four and possibly find a way to get the other 3 into a foster situation for an adoption place? ...and maybe have this organization help you with spaying the mother cat and either doing TNR (trap, neuter, release) or putting her through their adoption program?
Just a suggestion, I know everyone can't do what I do, but I did want to mention it in case it was do-able for you both.