<human>: Can you give me a shortened version of the text?

To give some background information: We live in the US and my sister (let's call her Jen) has a communication disability and has a below average IQ. She has problems understanding social cues and has never been in a relationship. She and a close friend frequented a grocery store owned by a family. One day, Jen told me that one of the workers there (let's call him David) was romantically interested in her. I eventually learned that he is in the country illegally. He has an expired visa and when I asked about his citizenship status, he replied that he will work on it. 

They have been dating for about 8 months now. David is very serious about getting married because he is 35 and wants to settle down with a family. He told Jen that he would like to get married within the next year. I am all for my sister being happy and finding a great man but David's situation and my sister's naivety/inexperience make it so much harder for me to find him to be genuine. I fear that he will take advantage of my sister, who doesn't know better. He wants to get lawfully married first and then have the reception when they save up enough money, according to my sister. My parents are supportive of them getting married because they want her to be taken care of by a husband. 

I had told her my feelings about this; however, in the end, this is her life and if this turns out to be a mistake, I will help her out. If it turns out great, then I will be relieved. Is this even something I should be intervening in? Is there anything I can advise her to do prior to getting married? Thoughts?
<bot>: my vulnerable sister is dating an illegal immigrant and I am scared he is only dating her to get a green card. What can I do for her?