Maybe I'm crazy but I find it a bit awkward

My bf's dad brings my bf's ex's kids to places we spend time at, like park, beach etc. Bf and his ex do have kids so the kids his dad brings would be their siblings and their mom only sees my bf's kids 2x a year. I find it weird and kind of awkward and feel like I'm taking someones place rather then being my bf's gf. Like I'm just a friend of the family. We have gone to another of bfs ex's because she married the ex's kids dad. It's kind of the only way all his ex's kids can see each other but I think his dad should grab bf's kids and take them there. Bfs dad still has a strong relationship with those kids and the other kids dad. Idk maybe I'm crazy or selfish but it makes me uncomfortable and I dont like it. I feel like I'm being adopted into the family not marrying. Bf and his ex were together 5 years. My sis said 5 years is a long time to just stop being a grandpa.