Can i be blunt? Why are you wanting/expecting them to make this journey? how will they get to LHR etc

I have recently had to manage a lot of travel for 8o year olds who have been very frequent travellers around the world for 20 years but now have health issues. I have taken a different view having travelled with them. They are frail and i have to ask if they are really benefiting from travel.

90 years old. Poland, wedding. Is it in their best interests to travel- you have said they are not frequent travellers. Insurance?

At a minimum you need to get them flying with family members who can manage them through the airport (stressful for those who take on this responsibility).