If they're both 6 months old now, I would try to set them on a potty schedule. Forget about the litter mat syndrome thing and just know that
any dog can be potty trained (and you must believe in it
)!!
If you're home with them, that's the easiest. Put them in their potty area according to a set schedule. Do you notice how often they go a day? If not, set something like every 5 hours (i.e. maybe in the morning, you take them to the patio, 5 hours later, you put them on the pee pad in an isolated area, 5 hours later, pee pad again, 5 hours later, take them for a walk outside and for potty etc...).
If you notice they don't potty on the pad, but have an accident, then put them on the pad every 5 minutes of their scheduled potty time. For example, if they don't pee, take them off the pad and wait 5 minutes watching them 100%. Put them back on the pad. Repeat until they potty. I know it's a huge hassle...but after several times, they'll get it. You just need to commit to this initial training stage and be strict about it. Only until you see a pee (or poo)
then you can let them roam a little bit without watching them like a hawk.
Once they keep to the schedule and you notice no accidents, you can gradually increase to every 5.5 hours, then every 6 hours etc.
The important thing to note is, you MUST prevent all accidents from happening. If it's near the 4 to 5 hour mark, pick them up or restrict the area they're in. For example, while potty training Casie, I'd keep her on the couch with me when it was an hour before her potty walk. If I let her roam, she'd sneak in an accident!
If it's 2 to 3 hours after she went potty, restrict her access to carpets. You NEED to make sure she NEVER pees on the carpet ever again. They more times she sneaks it in, the more she understands that it's okay. If you ever catch her in the act, give a firm NO! And then clean up with something like Nature's Miracle cleaner to get rid of the pee enzymes and smell.
In my home, I have hardwood floors with a couple mats. To prevent her from peeing on the mats, I had to take them all away. To prevent yours from peeing on your carpet, don't let her go there when you know she needs to go soon. And to know when she needs to go soon, stick to the potty schedule
Before you know it, they'll know the pee pad is the only place they should pee. Well, realistically, you need to stick to this until they're 1 years old (if you're like me and want them 100% house trained). If you don't mind an accident here or there, then you can loosen up the rules haha..
One last thing, the ability to hold in their potty for an hour of the number of months they are old they are doesn't always work. When Casie was 5 months old, she couldn't hold it for 4 hours. We had to start her potty schedule going every 2-3 hours. She was such a pain to potty train! I was pulling out my hair in frustration!
Good news is, Scottie is now 2.5 years and Casie just turned 1 year old in October. Scottie marks outside, so I had to be very careful with him and I didn't trust him until he was 1.5 years old. Casie has a teeny tiny bladder and can never hold it, but she finally learned very recently that she's only supposed to go in her designated potty pad area and outdoors.