Can someone knowledgeable read this jet2 holiday insurance caveat, please?

[Justmuddlingalong]

DP and I are due to go on a jet2 package holiday in 3 weeks and sadly DP's brother has taken ill suddenly and been diagnosed as terminally ill, just in the last 2 weeks. The holiday was booked in March, with insurance taken at the same time. Does this bit regarding "non travelling relatives" read as, a previously undiagnosed or treated illness will be covered and we could claim a refund? TIA

Yes but it may depend on their definition of close relative and the circumstances. One would expect it to include siblings but may just be parent or child.
Give them a ring and see what they say. You may get a refund or a postponement if that would suit you better.

Thanks for your advice. I'm going to phone them for advice because I can't quite get my head around the wording.