I think you handled that first conversation brilliantly. Your poor child, what a pickle.
One thing to find out urgently is if your dd is on meds that could be incompatible with pregnancy.
In her shoes i am sure i would be seeing this pregancy as a neat solution, after missing out on the post-A level pathways, a cute baby may feel like a direction and purpose for her. Plus if she is in love with her boyfriend... passion can be so strong at that age. Her boyfriend might feel differently when baby arrives. Or he might step up. Good idea to involve him and his parents so you can see which way the wind is likely to blow and keep him on message to stick around.
How about a round- table with BF and his family. To discuss where will baby live, how often can dd and baby stay at bf's house, can bf afford to learn to drive and get a car, what are the other GPs willing to do to help and support. All together, calmly, planning and not getting stressed ideally!
Then meantime at home you maintain that dd1 still needs to get a job and this is now urgent as she will need to start getting ready to support the baby. Pregnancy isnt an illness so if she was going to start work, she still must. The choice isnt "baby or a job because you missed out on education". She should be doing both baby AND a job.
If she is able to stand for long periods of time, hairdressing could be good - she can do it in people's homes and at odd hours eg evenings and weekends, which would mean her BF can babysit whilst she works. Don't let her make excuses, make her be practical. What jobs will work around a baby? She can get a basic minimum wage job for now until the baby arives then have a longer term plan ahead of her.
Babies can be very cheap as you can get almost everything free on Freecycle and FB if you ask kindly. Gently make sure your dd knows this will be a Budget Baby. Talk to her about reusable nappies and get her to research the costs and how you can soak and clean and dry them.
Get dd1 to think about her bedroom space. What will have to be got rid of, to fit the baby in? The main thing is the cot. Can dd1 sell some of her things to generate some money to buy things for the baby?
Dd2 i would worry about with a baby in the house. Can she go to a local libary to study at weekends? Would the BF's family let dd1 stay, or would relatives of yours do similar, for several weeks at a time if the baby is very disruptive at key times eg mocks and exams? Get dd1 to generate ideas, dont solve it all for her. This is her responsibility, and you are the safety net.
And make sure DD2 has the contraceptive injection.....