Awful idea, or feasible and fun?

You don't know how your baby will be (fussy and colicky or calm with a good sleep routine), but you do know yourselves. Are you and your partner the type who cope with eventualities easily, are you resiliant and supportive of each other, can you travel light (for yourselves)? Or are you already anxious travellers, worried about any unplanned changes, and find being away from home stressful? Probably somewhere inbetween. But you will have a better idea of you the two of you might cope.

I took dc1 between Edinburgh and London, on my own, at 8 weeks. It was the only way to see close family. And dh and I took dc2 to America at 12 weeks. As pp have said, it's easier at that age than when they are toddlers.

As others have said 4 months is a bit of a sweet spot where things are typically easy. Baby’s just coming out of the eat sleep poo phase and becoming a bit more interactive. But not needing solids or crawling. Everyone at the wedding will want a cuddle too! As long as you’ve got a car seat sorted you’re good.

if you’re not going to do this stuff at 4 months you’re not going anywhere til the kid is 6 years

It will be fine. Just hire a car at Edinburgh airport so you aren't reliant on taxis/public transport.

It's easily doable, especially if you hire a car and cut yourself some slack around staying to the end and being the perfect guest.

The fact you are describing getting there in the most convoluted way, it sounds like you are hoping to be told not to go. This is a mistake, it's easy to make your comfort zone too small with a baby, but it's better for your confidence and life to keep doing things.

I think it's doable, depending on the baby and how you're feeling.

I would definitely try and get a car though. Either drive down or rent one when you get there. Having your own space to retreat to/being able to nip back to your hotel/leave when you want will be much easier than relying on taxis in the middle of nowhere!

It’s entirely do-able all being well. Break it up into bite size chunks and rest stops (such as one night in Edinburgh before travelling onwards). I don’t think it’s unreasonable to be concerned about it either - you have to make the choice once you know your baby and how you are both adjusting to life together

Aside from logistics you know your friends but are you sure The Bride will be happy that you are seeing this as an opportunity for all of your friends to meet your baby?

Would the train be possible? It's much less stressful than going through the airport, you can all sit together round a table, if you book at the right time you can get first class tickets relatively cheaply and they bring you drinks and food round.

If destination is near somewhere on the Caledonian sleeper line that could work even better.

PS - I think we travelled to Belgium by train. Which I prefer generally, but especially with a baby and toddler.

Just do it if you want to go. What's the worst that can happen? Within reason, I think it is always best to give these things a go. Otherwise life starts to feel very dull and restricted.

We travelled to a friend's wedding in Belgium when DS was under 6 months and DD was not yet 2. I don't think we thought twice! DS was always an easy child, but DD was not! We were not able to stay at the venue, but the bride and groom were kind enough to let us put our children to sleep in their room (we borrowed a travel cot) as I think it was the only room there. Obviously we retrieved them when we left, before the bride and groom went to bed! So if you can set up something like that I would recommend it.

We also attended a couple of UK weddings (with some travelling involved) when DS was under 6 months old. It was a busy half year for weddings!

I think it will be fine. Much easier than with an older baby or toddler and you should have recovered/ feel well by 4 months.

Not sure which way we are voting AIBU or not but I personally would be planning to go as a first time mum. You just won't know how you will feel and how your baby will settle until nearer the time tbh. I have friends who would never do this and other such things whereas I absolutely would and would make the best of it/lower my expectations.

You realise that we're talking about a 4 months old right? They will not get bored at a wedding or need to unwind after travel... 🙄
They also don't really need a buggy (a sling is much easier), all hotels I've ever been to can provide a travel cot, feeding a baby that age is a non issue.

It’s doable. But do you really want to put yourself through it? Sounds like hell! Will you be breastfeeding?

Fine and perfectly doable. By 4 months you should have found your feet but baby won’t be mobile yet or old enough to need food or entertaining. Honestly, it’s probably about the ideal age to do anything travel wise because it’s about as easy as it gets before they come out the other side of the toddler years. The only point I’d make is that you drive then I’d rent a car over all those taxis or public transport it’s just more control over when you leave and if you want to take breaks to feed etc. But otherwise sounds fine.

I think if you didn't go, you would look back when your child is 1 year old and realize you can do so much less, and wish you had gone.

Honestly I would do it. Could you hire a car so not reliant on taxi/public transport? Make it a few days holiday so go up maybe a couple of days before, then leave day or so after the wedding? Maybe get holiday cottage rather than hotel? Babies that little are pretty portable.

It's hard to know without knowing the temperament of your baby, (which you obviously won't know until they're here)but I think its manageable. 4 months is an easy age to travel with because they aren't tiny, but they also aren't mobile so usually content just being held. Plus if you're both going, and only have one baby you can take turns it should be fine. We took our second on a 3 hour flight and a couple of long (2-3 hour) drives to visit family when she was 4 months, and I don't remember much of it so it must have been fine haha.

I think it's totally fine. Younger or older would be harder actually, 4 months old is relatively easy to travel with.
The only issue for me would be the transport from Edinburgh. The ideal would be to rent a car, is that an option? If you take a taxi you need to make sure they have a suitable car seat.
I wouldn't consider 3h public transport on my own with a baby after a flight personally. It's too much on 1 day.

As others have said it's hard to predict. Both mine would have been fine and 4 months is a really good age to travel imo (depending on baby obviously) as they're beyond new born age but still very portable and not on solids yet which helps. I think it will help if you have your DH/DP there with you who can take baby out if they cry and take on more of the baby care so that you can catch up with friends. If you plan to go alone with baby, I think that would be more tricky and you'd end up giving baby 80+% of your attention.

It might be worth hiring a car at Edinburgh so that you could drive to the venue and back to hotel etc on your own schedule rather than waiting for taxis etc.

I would only do this if another adult was driving. My baby wasnt good on a car seat and it would have been beyond stressful to be driving while he screamed in the back.

Weddings tend to be very boring for kids

A 4 month old baby will not be bored at a wedding!

can you rent a car?

You say "we" - is that you , your partner + baby?

I look at that stage as being (in practical terms) the easiest time to travel- baby is small, portable, doesnt need much entertainment, will sleep a lot, and won't need solids. If Breastfed, even easier!

A lot will depend, though, on how YOU feel - postpartum recovery, how feeding it going, etc - and how the baby is, jabs, etc.

What time of year would this be?

I think 4 months would be easier than with a newborn or a mobile baby/toddler.

So, it depends if you're going to avoid all these kinds of things indefinitely because it's too hard with a child, or whether you're prepared to put yourself through it. The reality is you won't know that until baby arrives.