Employment tribunal for Discrimination and constructive dismissal help

Hi everyone, I am new to all this so bear with me.  I need some advice if possible for my Partner. Sorry its long winded.

He has worked at his company for 25 years and  is Profoundly Deaf, he is constantly in a battle to get reasonable adjustments as he can't read English very well and uses Sign Language.  This situation has been ongoing since 2016.  They won't provide interpreters for him when he needs them, they don't include him in big meetings as they just give him a brief note on what they are going to say but he doesn't get to know what the other employees are saying and the answers to their questions.

It all came to a head in January 2021 as he was given a covid handbook that wasn't signed by an interpreter and other meetings where there wasnt an interpreter present but they just kept saying you will be fine.  In November 2020 he got Covid (we assume from his workplace where 2 others had already tested postive) he took a test because he was in my support bubble even though he didn't have any symptoms and went back to work to wait for his results.  In his book it didnt say anything about staying at home if you have a test or to wait for results, His Son had a test and went to work to wait for his results but he works for a different company, they handbook of Covid testing kit never said he had to stay at home to wait for results.  The problem here is we don't get information the same way as hearing people do as we are both deaf so rely on Sign language to get information.

He went back to work in January where he was presented with  a form to fill in, asked for an interpreter they said he would be fine so he said he is taking the form home to be translated for him.  The next day they gave him another form to fill in, he said again interpreter they said you will be fine so i ended up going into his work to translate the letter and to fill the form out for him.  Two days later he was called into the office again and given a note to say they are investigating and he needs to leave work now on full pay and gave him a letter to take home.  When he got home I had to translate the letter and it said he had been suspended pending an investigation.  We had to go to a disiplininary hearing and explained his side of things and saying there was no information or reasonable adjustments put into place to give him information but HR didn't seem to be interested and didn't understand Deafness.  It resulted in his suspension being dropped and to return to work whereas a week later they gave him a letter without an interpreter again and it said he was on a final warning for 12 months for gross misconduct.

He has now gone on the sick as the stress was too much for him to handle and wants to take them for disability discrimination but also Constructive dismissal as he feels he can no longer work here due the ongoing situation of not giving him an interpreter.  They have had 2 meetings with a representative in 2016 and 2018 to say he must have reasonable adjustments but they are just saying anything to finish the meeting and then still dont give him access to information.  He is now contacting ACAS as he doesn't want to do an early reconciliation as he feels he has done this twice already and he wants to leave.  

I appreciate any advice as he has been told by a representative that this is Indirect, Direct, harassment and not giving reasonable adjustments.  Can we fight this by ourselves?

Thanks