She is pressuring me because of her Jr Sis

so there is this girl (22yrs) that I was on a talking stage with this year, we later started dating and I even got to see her dad like 2 months ago for proper introduction. she has a jr sis that is 17yrs, currently in SS2. Her sister currently started dating a guy like 2 months ago. the guy is married (has 1 wife) and reside in their area. The guy said he wants to marry this girl within 6 months and wouldn't mind her writing her WAEC in his house . the problem is, now may gf is putting pressure on me to quickly send my parents, I feel she doesn't want her Jnr sis to get married before her, she is not even asking me on the plans. I wouldn't mind putting some of my plans on hold to plan the wedding in one year, but the fact that I'm doing all this becoz someone came with a firebrigade approach, it's making me reconsider. what's y'all take on this issue