In my experience trying many free ones, do you need a browser extension for one-click adding, or is just a mobile app for manually pasting links enough?

I have been thinking about your situation and I would suggest being quite careful with some of the smaller free apps you might find. A lot of them look sleek but they often have serious privacy flaws or they sell your contact list to third parties, which is a huge headache when you are just trying to share a list with family. Also, definitely make sure to check if the feature to hide purchased items is actually free. Some apps let you make the list for nothing but then they try to charge your friends a fee or force them to create a full profile just to mark something as bought. Since you mentioned being on a budget, I really recommend looking into the data policies first. One thing I have noticed is that some free apps stop syncing correctly if the list gets too long. Before I give my specific recommendation though, could you clarify if your sisters and friends are all on the same phone type? If you have a mix of Android and iPhone users, the syncing can get incredibly messy on certain platforms and I want to make sure I suggest something that actually works for everyone.