Where I'm from (Netherlands), there's a difference between being friendly co-workers at work, and being friends outside of work as well. The first one isn't that hard to reach, and I believe you're doing fine with it already. You say hi, and bye, and you chit-chat whenever there's a chance. The second stage is going to take some time or may never be reached because you're also depending on the other ladies' wishes with regards to being friends or not.
I still have some friends from my second job, I started that almost 10 years ago and worked there for 4 years. The same goes for my first programming job, the team was awesome and I'm still in regular contact (birthdays, meet-ups) with some of the guys. Yet, I recently joined a new team, and the people there seem to be keeping their jobs and their lives a lot more separated. I don't really think I'll be able to reach the levels of friendship I reached in other jobs. So the first thing I'd advise is to look around, and see if your wishes are actually realistic for the working environment you're in. If people are very professional and keeping their lives and jobs separated, it's at least going to take a lot longer, and a lot more effort, to extend this to where you're friends outside of work.
The first thing that jumps out at me is that you're only saying hi-bye, and have maybe had a few chit-chats with these ladies whenever you sat next to them (if not, your first step is to go do so). A simple 'Hi, how are you today?' is a much better start for a small chit-chat than just saying hi. Or, ask on Monday 'Hi, how was your weekend?'. These small conversation starters will hopefully give you some insight into what the ladies like, what they do with their time. If you're regularly helping them out, you could even ask if they're still ok, or if they need anything. Try to get past the hi-bye, to a level where you regularly chit-chat. An 'I'm going to have lunch, want to come too?' if you're having a designated area to have your lunches (even when brought from home) might be a starter in freeing up some time for chit-chat. make sure that the entire team feels free to come (extend your invitation to all of them instead of a specific person) and make sure to give attention to everyone around you, not just the two ladies.
I wrote this answer on Social Penetration Theory and self-disclosure a while back, and that's what you should be aiming for as well: Whenever there's time for chit-chat, slowly reveal a bit more of yourself, of your personal life, and if people react well (reciprocate), it seems like these ladies are open to more friendship. On that same note: I crochet a lot and have made little gifts for co-workers to reinforce a friendship, but random gifts may be experienced as weird if you're only on the level of saying 'hi-bye'. So, I'd advise against gifting your co-worker a painting, until they know you paint, seen some of your work, and have actually expressed some kind of wish for that sort of gift. Small steps!.
One thing that both of the jobs that landed me real-life friends had in common, was that the entire group of co-workers (even the ones I didn't stay friends with) regularly did stuff outside of the workplace. Things like all going to an amusement park, having dinner after working the story on a holiday, going out and having a few drinks after each sprint. People invited each other to go shopping, neighbourhood events, and to their birthday parties. In such a kind of environment, it's highly likely that if the entire group regularly does stuff, friendships develop and stay. So, to get to the point where you really can be friends with these ladies, try first to include them in the team. Go do something with the entire team, and look at whether or not these ladies are having fun, and seem to want to do this more often.
Just take it slow, don't be hasty. These kinds of relationships outside of work often take a few years to develop, so don't be disappointed if you're still not besties outside of work after 6 months or 2 years. As long as people seem interested in getting to know you better and keeping in contact with you, you're doing okay and can try to build on the friendship a little more each time.