Pressure

"On a scale of 1 to 10, how serious are you about my brother?" Was Mark's sister's question to me a few weeks back.
Naturally, having only dated the guy a month and some weeks at the time, I didn't know how to answer such a question. Was she asking if I would cheat on him? The answer to that is "No", Was she asking if I was in love with him? Again, "No", Was she asking if I wanted to live happily ever after and get married to him or if we're soul mates, or if he's the one for me and I the one for him? No comment, because I don't know those answers yet. That one question was loaded with so many possibilities it made my head spin.
Before and since this question was presented to me, playful comments have been made about me and Mark living together, getting married, things of that nature, and for the most part I thought it was teasing, and not an expectation.
Apparently, Mark's mother, having met and gotten to know me, and see me around her son, has decided that I am the one for him and we're eventually going to move in together, get married, and probably produce some offspring. From the way that Mark's sister acts and talks about his and my relationship, she feels the same way.
I feel an over abundance of outstandingly unnecessary pressure to stay with him at this point. Like, if I don't the world is going to implode on itself.
I mean, I know it won't and what happens, happens, and if we don't stay together, everything will be fine, and it wasn't meant to be.
But all the same, I can feel that pressure squeezing down on me. I really like Mark, and I don't want to break up with him any time soon, but honestly, can I get a little space with the guy over here? I feel a little choked. Especially since what proceeded Mark's sister's question was, "Have you guys done it yet?"
Again, how do I answer this. Why would she want to know? I told her no, and she said good, and that I should wait a REALLY long time. I think she's cock-blocking at this point but you never know.
I mean, I don't mind talking to her about Mark, but at some point this has GOT to stop.
This pressure is completely uncalled for to me, I mean, I've been dating him for two months. I am by no means ready for "Til Death Do You Part" or a "Happily Ever After" with him. I want things to be simple. Goodness knows we both deserve some simplicity in relationships at this point.
And for the most part "simple" is how we roll.
But his family worries me.