Endlers LIvebearers (Endler Guppy)

I have had these fish in the past and they did well, even with my not very hard water.
You say your water is 110 mg/l calcium - just to make certain, that's mg/l calcium, not mg/l calcium oxide (CaO) or calcium carbonate (CaCO₃)?

If it is just mg/l calcium, that is quite hard which is better for endlers than my water. 110 mg/l Ca = 275 ppm and 15 german deg (aka dH) Those last two units are the ones you'll find in fish profiles.

Male endlers are like all other male livebearers - they have 2 track minds - eating and breeding. They will try and mate with any other fish fish in the tank, male or female, endler or other species. They will display to each other by sort of curving their bodies and twitching or jerking their bodies. This is alarming when you first see it, but it is just male endlers being male endlers.
They will also play chase. They will all chase one fish, then suddenly change direction and chase another. It can look a bit aggressive till you realise they are not picking on the "chasee", and they never make contact.

As for tank mates, any fish that are happy in hard water and that are small enough not to eat endler males would be fine, with one exception - guppy females. The reason is simply that endlers and guppies are closely related and can interbreed. Since you have only male endlers, male guppies would be OK, it's just females you need to avoid.
With 70 litres, you should avoid the larger livebearers (swordtails and mollies) just on size grounds.There are a few non-livebearers that would go well in 70 litres eg emerald rasboras, also sold as Danio or Celestichthys erythromicron.