Cleaning, repointing(?) and resealing brick floor

I am trying to redo an old brick floor that is in my house. I would like some advice on how to do this.

Firstly the bricks appear to have been sealed with something a long time ago (see picture) any idea on what this is and how to remove it?

Secondly at lot of the mortar(?) between the bricks has become loose and fallen out so needs to be repaired or replaced. Should I remove the mortar between all of the bricks or just repair, but how? Apart from the amount of work involved in removing the mortar, some of the gaps are very small so I am not sure on how to remove it without damaging the brick sides.

Once the mortar is replaced/repaired I will need to clean and then reseal the brickwork any ideas on what to use?

You can use masking to protect bricks when filling joints.
As for removing sealer I don't know. Chemical striping I guess but I'm not sure that's worth the effort.
Good steam clean and wash.
Fill joins where needed.
Another sealer over.
Don't make it a big job

And advice on a sealer?

Find a sealer online and read the manufactures application sheet pdf.
Will advise on preparation and answer your questions.
If you don't like what it says look up another product

A customer of mine has a stone, not brick floor, that has become dirty over the years. From memory it has some kind of semi-wax finish. She did speak to her tiler. He said that he could use Methyl Chloride (paint stripper) to clean it, but he didn't want to work with the stuff over such a large area given that even with PPE you absorb it through your eyes/skin.

Have a chat with these guys.

LTP Sealer

They will send you some samples.
I've used to the purple label one on brick, think it was matt stone (usually for limestone).