Why are they not diagnosing dementia

Well, you can't have it both ways. Either you care about the human impact of throwing kids and MIL together for a holiday on them or you don't.

Ok - so really you need some way of convincing them of the reality that it will be a shit show and that MIL isn't fit for this holiday - it will undoubtedly be distressing for her. Can you arrange respite for her and give FIL a break? Or can your DH stay behind with her? Or is he is denial and thinking everything is going to be ok?

Honestly, if I was told in advance that someone in your MIL's condition was going to be on a flight with me - I'd change my plans - different time, date, airline. It would be horrible to be on a plane with someone actively hallucinating and in addition, if that happens, the flight will probably be diverted to get her off and into hospital.

I wouldn't go - will be a miserable holiday and even in the best case scenario you'll always be on edge with uncertainty.

I agree with this - it seems to be the only thing you can control in what it surely going to be disastrous and very possibly also traumatic and expensive as I suspect they've not fully disclosed for the travel insurance. Don't go, don't let the children go.

Before my DF was even diagnosed with Alzheimers my DM was determined to go on holiday abroad - just the two of them. Because it was an early flight they stayed in airport hotel the night before. DM has said very little about what happened, and now would probably deny all of it, but they came back home the next day, without even attempting to get their flight - and my DM was surprised that no one was surprised that it had ended that way.

I don't see how the OP's MIL will even cope with the airport, never mind actually being on a flight. Sorry, but this is a stupid idea (as the OP can see) and is going to end very badly.

You can’t go on holiday with them. It is a disaster waiting to happen.

I appreciate your FIL is desperate for a break but he isnt thinking clearly. And it is very very unfair on your MIL. Taking her out of her familiar surroundings, taking her through airports and on planes and to an unfamiliar location is totally unfair.

And I would reckon any travel insurance will be invalid if they haven’t been honest about her situation.

My Mum had Lewy Bodies dementia. It’s not an easy one to get diagnosed sometimes.

Ask to see the documents, I would seriously not go with them, let dh go on his own and he can be her carer and take responsibility for them

Insurance won’t be valid.

Seriously. Just say you and the kids aren't going. You'll have a holiday at home. It's the only way and the only thing in your control.

No medical professional would say someone will remain stable. Having delusions, possible paranoia, advanced parkinsonism all need to be declared, it is then up to the airline if they refuse to take a passenger who could potentially come to harm or harm others. She would need extensive medical insurance and a fit to fly certificate. Anything less is irresponsible and unfair on everyone including mil.

DO NOT go on holiday with her.

Medics see DM for 7 min when she’s on best behaviour (automatic). You know her.

There’ll be a crisis and an 🚑 . Been there, done it.

On the upside you can send the ambo with her in it straight back to the Parkinson’s nurse who’ll have to look after for a month in hospital.

Hrumph. Good luck OP.

I found doctors reluctant to acknowledge DB’s problems - maybe because there’s no cure or magic medication.

Your only real option here is to decide that you and the kids aren't going on holiday. So... I'd do that. Don't expect to be thanked for it, in fact if MIL fails to cope with a change in location, as seems quite likely, there will probably be dark muttering about how it wouldn't have happened if you were there, however illogical. But if you're concerned about the impact on your kids and indeed on MIL, then it's the right thing to do.

Ask DH what will his plan on the plane. He is a aware not disclosing this will invalidate her insurance so has he hundreds of thousands are.aside for reparation privately if she gets banned.

I wouldn't be going ans neither would my children. It isn't fair but not disclosing this to medical and airline is negligence.

I appreciate I am thinking worse case scenario but very conscious that this is a disaster waiting to happen

There is the Montreal cognitive assessment test which you can download and see what sort of tests are sat.
i think she will be totally confused in strange surroundings. And more at risk of falls. Who will be looking after her while DF ‘enjoys’ his holiday? I assume DH.

Your updates indicate it is absolutely necessary to have a frank discussion with the family and medical team. What on earth is the plan if an episode occurs on the plane?

What also needs to be sorted is a break for FIL he may be in survivor mode a break may help him gain perspective.

What could a GP say that a specialist nurse hasn't? IF dh and FIL have been honest, the nurse appears to be saying that symptoms that are currently stable will definitely remain stable when travelling. I think that's a big statement but a GP is not going to actively contradict that?

Right.

First of all your hands are not tied. You can say that you are not prepared to travel with her while her symptoms are not under control - for her sake and your sake as a group.

It's hard to be the bitch who says no. But you can. Cancel the whole thing, or one parent goes with FIL the kids and the other stays behind with MIL. An alternative would be respite for her, but that would probably also result in disorientation for her and possibly a hospital admission.

Then do you have a contact number for the Parkinsons nurse, or a name? Ring or email them, telling your husband you're doing it. Say you're looking for guidance on the holiday decision only. Tell them all the symptoms that concern you and ask how to manage them. They may or may not engage wuth you but the response should tell you if your DH and FIL have been honest.

With the holiday zi would ask the gp for a fit to fly certificate, what happens if she becomes agitated, distressed and confused on the plane or at the resort. Your dh can speak to the gp with his concerns, does anyone have power of attorney.