Unfortunately, yes your girls are seniors now. And for the most part they are going to sleep. Our girl Fuzzy Rat loved to climb trees, chase kids and jump into the lake for a swim, in her prime she could jog at heel for over half a mile. By her second summer she would hang out in a tree when we lifted her up into one, only swim straight to shore and weebled back to the car after sitting around the park bench with me. She was one of those weird rats that slept with her eyes part open, so I don't know if she was always sleeping but more or less she was inactive. Our big girl Cloud is pretty much a little over a year and a half now and she's a pudgy napping blob most of the time too.
It almost seems to happen overnight... one day your girls are flying around playing and exploring everything, climbing, chasing and generally little balls of energy... and then they just run out of gas and start coasting. Don't take me wrong, Fuzzy Rat always enjoyed a day out, but as her abilities faded so did her confidence. Rather than scurry off to explore on her own she would stay closer to us and as soon as it got dark she would head straight for the car or the house.
What you are describing is pretty much normal, especially if your girls are already getting pudgy.
We kept Fuzzy Rat going by taking her out with us and pretty much carrying her around. She still liked to meet people and see new things, but by her third summer, she would mostly nap in the clovers or on the bench next to me. She loved crowds and would perk up when she met new people, especially kids, but the days of the intrepid adventurer were well behind her... She was a senior citizen and sometimes she would even get disoriented and you could actually see her eyes fog up.
Try to keep your girls engaged and help them to do things they like, it will extend their lives.... but yes... most of the time they are going to be napping.