Thank you. It seems like you are right. After you gave me the names to search, I googled further and found this photo. The photo for pattypan squash closely matching to what I have - even shapes of the buds

This discussion might be of interest: https://www.houzz.com/discussions/echeveria-pulvinata-e-harmsii-or-e-doris-taylor-dsvw-vd~4598521

Don't just put plants under the lights suddenly. They are starved for light - so were probably in low light for a while. They will burn if you just give them too much all of sudden. Best practice is to acclimatize plants to new environment. I do not grow red plant, so will not suggest anything regarding pruning, but recommend same for light as for Kalanchoe. Kalanchoe stems could be cut into few pieces, leaving some stem with the roots and at few leaves and it should continue growing. I would suggest adding more perlite to a mix it is panted in, and using containers with drainage holes. All of the pruning will not help unless you get supplemental lights. Use grow light if you want to buy it. If trying to save $ (and have only very few plants), you could use ordinary CFL bulbs (23W, 6500k). Put them about foot or more above the plants to begin with, lowering inch or two every few days. Light should end up as close as possible without burning plants - if you put your hand just on top of plant, you shouldn't feel burning. 12 -14hrs/day is good.

If anything it looks like a bit like Hibiscus syriacus to me. Although the seeds don’t seem right. But fairly sure it’s something in the Malvaceae. It isn't a plum and honestly looks nothing like one. And it definitely isn’t mangosteen.