Can anyone advise me on my current dilemma?

I have a friend who is moving back to the UK and has an outdoor cat. He had his innoculations and has had "the op" and has been living quite happily at their villa. However, now he is faced with being moved to the flat above their bar with my friend´s daughter. I don´t think he will be very safe at the flat as it is in the middle of the town and he is used to the countryside. With the hot weather here being 35 degrees the windows will be open so inevitably he is going to wander outside into the more dangerous environment.

An alternative is for me to have him here with me until they decide if the move to the UK will be a permanent one (and they arrange a pet passport). I have four kitties who have always been indoors. Due to financial issues they have never been innoculated so I am worried about introducing "Felix" into the household with them not having been outside or having built any immunity.

As he had been innoculated and is in good health (with a very healthy appetite!) would it be okay to have him stay with me without risk of infection? The cost of innoculating my four will be 45 euros each - money I simply don´t have. I believe that he would be infinitely safer with me and will no doubt settle in okay as he did have a trouble-free visit a year ago.

Any comments / suggestions would be appreciated! I am in a dilemma as I want to ensure the good health of my four kitty companions but am also concerned for Felix´s long-term welfare. He is such a sweet cat and they have had him since he was 3 months old.