School & nursery on a bike with 2 children in London, what are my options?

[confusedperson]

It sounds complicated but I really want to make it work. DS1 (4.5yo) got accepted into school which is opposite direction to the train station I go to work from and 25 mins walking from home or almost 2 miles car ride. There is no bus going to to the school direction. Taking DS1 on a bike would take 10 mins and majority of the route is off-road or on back roads.
I also have DS2 (18 months) who will go into nursery which is in between home-train station. About 0.3 miles from home.
I would need to take DS1 to school and collect both DS1 and DS2 from school/nursery. DH works too far away to make it in time.

I am inexperienced biker but this is always I wanted to do and I think this is a very good time to start practice.

The best I can think of was getting a rear child seat for DS1 (the one for 5-10 years old), bike him to school, then park the bike on the train station. After coming from work collect DS1, then go back to the nursery and from nursery push the bike by hand and let DS1 push DS2's buggy.
Another option would be to get tag along bike for DS1 and a front seat for DS2, but in that case it is risky to leave all it on the train station and too inconvenient to leave at home.
Trailer is not an option because I live in Victorian terrace (no space in doorway) and not possible to park on the train station.
DS1 is very tall for his age, but can barely ride a bike with stabilisers, I think it will take a couple of years until he learns to be independent rider.
Two seats on a bike would be ideal, but I too inexperienced to be able to handle this.
A cargo bike wouldn't fit through my doorway and no chance to park on the station.

I know it all sounds complicated but I really really want to work. What are my best options?

Chariot Cougar trailer collapses fairly easily if you have cupboard space for it (wheels off & then folds flat). So you could take DS1 to school and then leave trailer at nursery/school depending on what works.

Big advantage for inexperienced cyclist is that they are likely to be fine even if you fall off, as trailer bike connector means that bike can fall over but trailer still fine. Disadvantage would be that 4.5yo might outgrow quickly and not cheap.
Sorry can't think of better solution.

I work at a day nursery and we had a parent a couple of years back in the same situation. He bought a tandem bike, school child sat on the back seat and nursery child was in a child seat at the back.
Child seat detached and was left with buggies at nursery all day.
HTH

Thank you for replies.
I just looked at trailers on ebay, and a collapsable trailer would be a quite a good idea, but my 4.5 yo wears 5-6yo clothes so I am assuming it will not be a good fit.
Tandem bike could be an option if it is easy to park them publicly.

Yesterday, I was surprised to see that my 4.5yo can ride easily for an hour, but we have nowhere to leave his bike - we cannot leave it at school because we will collect him from afterschool club from different location.

Leaving a childseat at nursery would be possible, I guess...

No bright ideas here - DS1 (same age as yours) has outgrown the bike seat and is getting cramped in the trailer. Can you tell me about 5-10 yo bike seats?

If you find a solution, try Outspoken Cycles (or Sustans or local council) for cycling training, route planning etc to give you confidence.

BlueChampagne, the 5-10yo seat is Bobike Junior, but I only saw it on internet.
I myself purchased Bobike Maxi from ebay. It fits OK to the bum of my 4.5yo DS1, but his legs are almost (but not yet) in a way of my pedalling. I can still pedal with him but not for long.. 6 months at max!!
Not to mention that DS1 weighs 20kg already and will outgrow Bobike Maxi limit soon.
While this will work for few months, I am looking for other options: 1) expensive tag-along Roland add+ 2) expensive trail a bike FollowMe 3) cheaper option of DS learning to ride properly and without stabilisers and take our time to SLOWLY cycle to school every day.

What about a Yuba Mundo? I'm currently drooling over one to become my bike solution . It's a long bike that's not that much longer than a normal bike but can fit 2 bike seats (or one older kid sitting on the back plus the younger in a child seat). It is supposed to be pretty stable to ride as its designed to carry 100kg on the back (if you wanted to!). There's a bike shop in London bridge where you can try them out - can ask DH if you like cos I've forgotten the name.

We got a Burley trailer off eBay which collapses in seconds but it's a squash already for the two DCs (3 and 1.5) which is why I'm trying to think of a better space saving solution. I love cargo bikes like Christianias but so impractical in a flat!