Damned pregnancy hormones! As pp has said it's normal to feel protective, however the portacot could really come in handy if you are there and bubs needs a sleep. You also don't know what may happen, you may need them to look after bubs in an emergency. Just let them be happy to have it, there is nothing forcing you to leave bubs with them.
In regards to the vaccine, I personally feel this is quite selfish of them to refuse so I can understand your frustration. Perhaps it's a matter of lack of education? Give them stats to read about the reemergence of whooping cough epidemics.