Hi Victoria,
First don't worry. Each dog can be house trained and your little friends too. If you give some more information how you are trying to teach them where to go we can give you more specific advises.
You said that you take them out on the patio and at the same time you have pee pads. I thing this is not the right way. You should choose if you would like to teach them to go out or you prefer pee pads, but choose only one. Otherwise you are confusing them and the house training process might continue too long. If you decide to take them out choose only one place and take them only there. That way they will understand faster.
Also take them out every morning as soon as you wake up, after each meal and after playing with them.
Also after sleep.
When they pee or poo outside give them lots of prizes and treats.
Yes it's hard but if you are consistent they will understand very fast.
Here there are lots of tips about house training