Replace or Repair Floor Joists

[NatB]

Hi guys
Recently ripped out an old floor which wasn't put down well and which had also been damaged by a leak I'm now left with a few joists that look they have warped and twisted, one of which has slight movement also.

Ripping out the joists and replacing them isn't really a road I want to go down unless I really have to (new kitchen underneath). It's a 1st floor room in a storey house. The new floor will be tiles and I was planning to noggin the existing joints prior to putting down 18mm ply and a latex leveller afterwards as it's fairly uneven across the joists.

My question is whether that will be ok with the current state of the joists or do I need to do further work before that?

Also, the room contains the two boilers for the house thus a lot of pipework is in their. When putting down the floor is it worth cutting out a section where the boiler pipes enter and leave the floor as an access point or should I only really worry about access to the pipes directly below the boiler?