Have had this both for +10 years, recently i have noticed that the base of the cacti is turning brownish and i think it might be rotting, the big one gets watered like twice a month but its just really some breeze i make with the hose, however the second was moved to another place and had more water and less sun for about 2 weeks, after noticing the brownish i moved it back again next to the big one. Should i worry? will it fix itself?

If they're soft (and they look that way) then I think they're already gone. Don't give up prematurely, but temper your expectations.

Water consistently, deeply, and infrequently. The soil should go bone dry at depth every time. Strong light is important (hours of daily sun) but keep your plants out of direct midday sun while they're in some kind of apparent crisis.

thanks for the reply, i dont know how soft is soft, to put some comparison they feel like a ripe grape (the big one being a little bit harder than the small one), it is not very visible in the photo, but the big one haves the typical blue-green color, is the right corner the part that is a little browinsh, also it flowered a week ago.

So, i should keep them out of the light of middle day and water them (infrequently)?

Yes. You should know pretty soon whether they are gone or there is still hope.