He is a trier.

I hesitate to add to the 'week from hell', and I hope you can find some time to recover from it all.
However, I can't let a post like this go by without adding my 2 penn'orth to those saying 'keep your eye on the ball'.
People like Aepgirl's aunt sound harmless if irritating. If their 'dad' makes a fuss around some people, being a bit bumptious, it probably does your GCs no harm. We've all known people like that!
But if he pretends serious knowledge he doesn't have, or seems to be role modelling lying, then I would be keep a note of it, not to tackle now, but to use if necessary in the future.
I hope he is just, to use an old-fashioned phrase 'a barrack room lawyer'.

He's insecure so resorts to childish boasting. Just nod when he starts up!

I would be tempted to say in a jokey way,' Well, when you've passed your test, you can comment on my driving. When you've qualified as an electrician/doctor or whatever, you can diagnose my medical condition, come and repair my electrics etc.' It may just shut him up for a bit if he knows you are fed up with hearing his comments.

He may genuinely know all this stuff (exception is driving without a licence which is just plain criminal). But anyone can read the same stuff that doctors and electricians learn from, the only difference is they've taken exams to prove they've read it. So any lay person can know just enough electrics to wire their normal house, and just enough medicine to tell the difference between appendicitis and norovirus.

I didn't get the impression that he is actually driving without a license, rather that he is a 'back seat driver' and knows better than anyone about cars, driving, road conditions etc.

No he doesn't drive, just a back seat one.

I fully understand Nannawind why this gets your goat!

Airing it here is far, far better than commenting upon it to family, which you know, and don't do.

Sounds to me as if your DD's partner has a very large chip on his shoulder and boasts of all the things he can do (and perhaps some he can't) to impress.

As far as possible, let it go in the one ear and out the other.

If he is actually doing electrical work in the home that it is illegal to do unless one is a qualified electrician, driving without a licence or treating people without the proper medical qualifications, then he is breaking the law.

However, if you try to take the matter up with him, it will lead to one almighty family row, as like as not. If he is just saying he can do all these things better than those who have studied the subjects, then it's annoying, but try just to change the subject when he starts.

Yeah you used to be allowed to do electrics as long as it was checked off by a qualified person. There are still some you can do at home. I am not sure where the threshold is though

Anyone who can put up with a back seat driver deserves a medal.

Yes, you still can do certain electrical work, and some has to be checked off by a qualified electrician. There are some details on gov.uk and your local building inspector can deal with more specific queries.
I only add this because I happen to know, and it has been mentioned.

If I were you Nanawind I would count my blessings that your daughter has someone who loves her, and she is not on her own with three kids to raise.

So, this guy is a Jack-Of-All-Trades-But-Master-Of-Non? Knows about everything but presumably has no qualifications or proper training to back it all up? If he's driving around with no license it would make me wonder what else he gets up to that's 'under the police radar'.......He sounds a right Jack The Lad!

And so were the Kray Twins.

Please note he doesn't drive just comments from the back seat. Read my post properly.

That's not a nice post Margs
The Kray twins were gangsters and criminals.

This man does sound like someone I knew - we nicknamed him Walter Mitty.

Agree with Sodapop - Sounds like he's trying to impress - perhaps you could try a little flattery and he will then feel more confident?