I have a friend who's twins self-weaned at 3 years old, it is perfectly possible to bf twins, two babies, two boobs, feed them together, job done!
She needs to see a bf expert, not just a MW or HV. Get hold of her local LLL, ABM etc and ask for a home visit, she needs to get thier latch checked and get some good practical support with things like positioning etc. Topping up and expressing (ie giving bottle feeds, or even using a dummy) will possibley be detrimental as it can make them latch badly, so until they are feeding well and latching easily don't give bottles, even if they have ebm in them.
She needs to get this cracked in the next 4 weeks so that she has it sussed when her DH goes back to work. FF twins may be easy when you have a helper, but it is impossible to hold and bottle feed two babies simultaneously, not to mention the number of bottles she'll have to wash, sterilise, mix etc, so, long term, bf is easier, as she can feed them by herself with no help. If she perfects the double rugby ball hold on a good nursing pillow she can even read a book or eat whilst the babies are feeding!
Tell her to hang in there, and to expect to spend the next few weeks sitting down with her babies feeding almost constantly. If she demand feeds them like this her milk supply will match thier needs. Her body knows she has got two babies to feed, and can make enough milk for them as long as she gives it the chance. She needs to believe in herself and not to feel that formula is the answer. She has the good-stuff on tap, don't let the dimwit HV erode her confidence.