Help with cacti care and identification

[Vsunflower]

Hello, I have 2 pots with cacti and I want to save them from dying, It looks all brown on one side (it's been facing the window there but I live in a cold place so not much sun during winter)
And over all the health of the cacti look poorly, how can I save it?
How should I repot it?
What are the hardened brown parts at the bottom of the cacti?
And what species is it?
They flower and are green on one side of them As well as having those new black little puffs so didn't realize how bad looking they were and have forgotten to repot them. Its embarrassing how poorly I have taken care of them but aiming to do a better job from now on.

Thank you in advance,
I know I haven't taken very good care of it but I will from now on. I got it from my grandma many years ago.

[teo]

It is an Echinopsis (oxygona?). The hard, brown part is just natural corking due to age. I would repot them in a slightly larger pot and a bit deeper in a good draining soil