I don't think pot is doing it - but it probably wants that sunshine outside.

What is the potting mix, and does the pot have a hole in the bottom?

It is sitting on opened window south facing. Not enough? It is in 50/50 perlite and c&s soil. And yes it does have a drainage hole. Same with sunburst I posted recently with flower stalk never bloom or grow more taller dries out fast, in same 50/50 mix and Eve's needle cactus, all in same size pot, mix. Which is why I decided to not replant my domino cacti, waiting after it blooms any time now.

Ya I'm thinking not enough light either. Doesn't look dehydrated. These guys need a good amount of sun to get nice tight straight growth. I've seen a lot of pics online of people who have grown these inside, and have issues with not enough light:).

Is there anywhere you can put outside?

Kara- I could not place them outside cause I'm living in city so all these building blocking. If my window was facing east-southeast it would probably get full sun. So only strongest sun is south facing with midday sun and then all day after that. Will I need to supplement them with growth light? Or should I move them back n forth between east (morning sun) and south?

Socks- I'm sure they'll so happy if I have that spot where they'll receive full sun unfortunately I don't have one :( I'm in zone 5 though.

Put it in as much sun as possible. Those are large, outdoor succulents actually, I'm always surprised that they get sold as potplants. They need full sun all day to grow as they should

I'm in Northern New York - my flappy goes out on the patio at the end of May and stays through September. Full sun. During the winter it's in an east facing window, but it doesn't perk up and color up until it goes outdoors.

So should I supplement them with lights? Since I have no spot for them to be in full sun.

yes though doubt that will be enough light... many (maybe even most?) succulents need maximum light to be healthy and do well... indoor lighting is a poor substitute, but certainly better than nothing... get lights with some UV spectrum and put close to plant (right above) for best results. No window sills in your home?

Palmbob- yes they are sitting on south facing opened windowsill.