If she's trading her Baron title away, you don't get two landmasses to combine, you get either a town or city (whichever you choose). She gives up her settlement with her title.

If she keeps her title, then you have separate settlements.

Towns and strongholds are pre-placed. The only way you can combine them is by building one from scratch nearby, and hope the Duke is willing to help pay for that stronghold. Remember, a military baron signs a contract with the duke to pay for the stronghold and the garrison.

If you want to build a castle in your city, you can do that, but the duke probably won't pay for it. It will be very expensive.

If you want to build a city around your castle, it may be subject to siege and a lot of damage, and make it harder to defend.

my advice to you is to get your wife to gift you the second pledge giving you more IP wich will mean you will pick your settlment before barons with only one pledge and you'll be able to pick the biggest settlement after the count

Don't forget, you can have a lot of your friends buy villager tokens, and give it to you as a way of increasing your land mass holdings also.

In short no the cities that go with the Baron tier are pregenerated and won't be on top of each other. Likely close if you are in the same county but each town requires certain amount of supplies (food water ect) to sustain it. So even if you build a second town nearby with tons of ip eventually one or both will die out.

Course you could always work out a deal with your count to have him/her help you by building roads and other amenities to help your towns stay connected.

Now if you were both say counts, it would be possible to join your counties together as a "super county" a term coined by a certain feline member of a certain duchy in the west.

While kingdoms, duchies, and counties are just lines on the map, towns are physical things that must have room to breathe.

If you REALLY wanted to I suppose it may be possible to gradually expand your towns closer and closer to each other and then use management tables to redraw borders and maybe combine them entirely? You might also be able to give one heir 2 titles but you would have to wait until our first 2 characters die of course.