28F, 34M Is this Perhaps Weird?

Hi everyone I’m new not to only posting here but to relationship as well.

I have a crush or rather like a guy for a very long time and we seem to get a long very well no questions asked. We have a situation where if we have to date is because we’re serious about it. So we are sort of rearranging our lives accordingly. I’ve always lived alone in my apartment and he has been living with his parents. He moved out now and moved into an apartment he bought everything else is stable. We might end up together? Maybe not sure that’s what it looks like🙈. And it seem it might be end of this year. (I wish I can explain more here). It is established we both like each other.

The thing is for the past maybe three year his sister befriended me we are the same age we started off with being acquaintances until we became very close. She doesn’t know I like his brother, we’ve never talked about it. Or maybe the brother did. I always had a rule to not get involved with families until things are official but this is different because through her I met the mother and some of the sisters as well. And either way I feel my friendship to her has nothing to do with her brother.

Will it be weird if she later finds out that I have liked her brother this whole time and never mentioned it to her ? Do I tell her or it’s not going to be a problem? I’ve seen similar situations that end up bringing a rift between friendships and boyfriends etc due to similar cases. I like her a lot and I don’t get to make quite a number of friends it very rare.

What do you all think?