Welcome to the forum Milena although I'm sorry about about your dad.
It's completely understandable why you want to be with your family and help your mum at this time but unfortunately we can't answer this question.
The best thing to do is pop on the gov.uk website as you will find all the latest update to date information and advice regarding travel to Poland at this time.
I hope this helps but if you have any more questions relating to your father's health it may be best to give one of our cancer nurses a call on 0808 800 4040. Their phone lines are open Monday - Friday between 9a.m - 5p.m.
