Neglected Cacti

Hey everyone.

I am new to cacti and I found these cacti at my parents house. They are quite old and have been neglected for years. They have not been watered or reported since they were bought 5+ years ago!

I want to know what people suggest I do to help the cactus thrive again. I have attached a couple of pictures for you. It appears some parts are dead and some are dying. Should I pot them again in cacti and succulent potting mix and remove the dead parts?

Thank you!

 

I think you have three different cacti in the same pot there.
Possibly four.
I'd be inclined to put them in separate pots in some new compost.
You can cut off any obviously dead parts,but only one appears to have been badly affected.