Ceiling joists which are not continuous or joined

I have recently taken up some of the boarding in the attic (put down by previous owners), in order to make a larger loft hatch to make it easier to get things up there to store. The hatch will be in the centre of the building, on the upstairs landing. There are 2 loading bearing walls either side, and the hallway is about 0.8-0.9m wide. In cutting back the over-boarding surrounding the new opening, I have gained visibility of 2 ceiling joists (A & B) which will sit at either end of my new opening. Joist A (https://imgur.com/WVjJoE8) is not continuous, but has an overlap of about 3cm (with I think 1 nail joining them)! Joist B (https://imgur.com/6NjKVME) has no overlap at all, and is offset from its opposite number by 5-6cm. I order to effectively distribute the tension loading which will be reallocated by creating my opening, I need to effectively join these two joists. Can joist A be 'built up on either side to make a larger 'lap joint', and then sistered? If so, how far back over the load bearing walls either side of the hallway do the built up sections need to span? For joist B, the easiest way to join would be to run a 2-3m C16 2x4" between the 2 existing joins (because the offset is so large), and then coach bolt the overlap on either end with 3-4x M10 bolts to join the currently unconnected sections. Is this a compliant way of making the join? If so, what overlap would I need on either side? I'm based in Kent, UK - and I'm due to have building control visiting for a inspection of a separate issue in the next month. So it's important to me that these corrections are made compliantly. Any direction is appreciated.