I myself a step mom of 3 kiddos and an immigrant. Initially when I met my husband I was scared to meet the kiddos since I have never before dated anyone with kids and here I have all 3. My husband always came up with different ideas how we all can hang out and do things together as a family like camping trips or going to a pool. I homeschooled my kiddos during pandemic and yes it was tough and we would go insane and it's also time when we got married. Living together and having kids every other day made it hard for us -being a young couple. But to be honest, one thing that is really helpful is to think that your fiancee is coming from a different culture, perspective of blended families is a way different in developing societies. Here yes everyone is open and try to be friends... But even I have my boundaries with everyone and especially with kids’ mom.
Reading your story really reminded me of me when we just got married and pandemic peacked I was also hiding in a bedroom after kids’ schooling because I needed some time alone not because I ignored everyone I just love my privacy too much. I would suggest having a conversation with your fiancee ask her how she sees your lives together, what are her thoughts. As a stepmom I am still learning and I probably will fail to understand much but every failure is a lesson. As I await my own baby, I am sure I will understand it even more when I become a mother of my own child. Just really have a talk and discuss with her, it might be so hard for her to understand the blended family dynamic, and she maybe needs someone to help her. I also have a youngest one the same age as yours, she will turn 9 soon, and I struggled with her and it also seemed that we both fought for daddy’s attention. But she also outgrew this and I love spending time with her, she has friends and does extracurricular activities. Anyways, no one would understand what step parenting is unless you're one. You do have to be selfless but also boundaries matter.