Is there a rush to get married?
If you think because you two have love for one another that you must run off and make it a legal arrangement, by all means do so, as it sounds like you care a great deal for her and about her children.
If there isn't a rush, take your time, love her the best you're able, and try to enjoy it- without worrying about what your folks think, or what society thinks.
I think you're a very brave man
