I understand your position, having a 15 month old girl is difficult for me (i ran out of energy
sometimes ) I can't imaging having two!!!
Catalina made me a huge mess today at lunch time eating her yogurt using spoon,but I think sooner or later this has to happen.
she is being using a baby spoon for the last month, I started just giving her the spoon to play with(no food) just to get her familiar with it, so she will chew on it,put it in her mouth ..etc.
Next step I did giving her solid food, like cooked rice...just a little bit in her plate ..so she doesn't get to messy.
Then since the last week i started giving her liquid food like yougurt... and of course she is making a mess...but it is ok....because she needs to practice to became a better spoon user.
I have to say she does really good with solid food, like rice, or any kind of dry food,she eats at dinner time with us,chicken or meat..etc.
What I will suggest is to start giving them a baby spoon(there are some made form wood (we have that one) or also they have plastic too) and let thm play with it and let them practice to put it in their mouths.
Good luck my friend, it is a process but like somebody say to me . " the sooner the better for you because they became independient, and it is nice to enjoy your dinner with both hands in stead of one" if they can feed themselfs you can dedicate time to eat and relax too.