Should I hand flat keys to executors of will?

Hello everyone
Can anyone give me a bit of legal advice or share their experience to help me?
In my dad's will my brother and I were named as executors. I have great difficulties in dealing with my brother so I contacted the firm that my dad made his will with and asked them to take over the role of being executors. My brother was very happy to leave this task to someone else and so we signed over executorship (is that a word?) to this firm who I thought was a firm of solicitors but later turned out to be an elderly couple with some experience of drawing up wills and dealing with probate.
I am worried about the people who we appointed. There were a number of red flags but I don't know if I am being unreasonable.
The probate certificate was granted several months ago but I still get my dad's old bank, and various financial companies where my dad held money, as well as his utility companies and landlord, writing to me asking me to supply various certificates for over six months. I think this is because I had power of attorney for the past few years but was worried that our executors were not doing their job.
I recently asked the executors if they could send me a brief summary of who they have contacted and how things are going in terms of dealing with the estate.
They wrote back saying they could not tell me because it would cost me money for them to write to me to inform me of every step of the probate process. I said I just wanted a rough idea not a detailed step by step account, but they did not reply.
They also changed their official correspondence address. I got suspicious and then realised that they were not solicitors as we had thought but were 'probate specialists' . However in conversations with me and my brother they clearly allowed us to believe they were solicitors and did not explain that they were not until I confronted them with it. So there were several 'red flags' for me, I have not listed them all.
Otherwise the main gentleman we've dealt with acting as our executor seems charming in person.
However he wanted me to hand over the keys to my dad's flat two months ago when it was still full of valuables and I was still half living there to sort through my dad's many belongings.
He said he needed the keys so he could sell the flat. I felt very uneasy about this so I have made various excuses why I could hand over the keys yet.
Then he told me that I had to completely clear the flat before he could sell it and gave me a month to do this. I could not meet his deadline, plus I still do not understand why I need to hand over the keys or completely empty the flat selling it via an estate agent.
These people are still pressurising me to hand over the keys to them. I have put them off for another month while I sort through things to give away, sell or dispose of. This is my family home where I was my dad's carer, although I have my own separate home, I am used spending a lot of time in my dad's flat doing general maintenance.
The long and the short of it is that I do not feel comfortable handing over the keys to these people.
Do they legally have to sell the flat?
My brother and I just don't understand and we would rather give the keys to an estate agent to sell the flat. I would prefer the flat to still have a few basic bits of furniture, cleaning things, vacuum cleaner, and kettle in it, so I can still still visit the flat and maintain it, maybe give it a lick of paint, while we are waiting for the sale to complete. Then once the flat is sold my plan is to get it cleared completely.
Our executor wants a totally empty flat, containing only carpets, and they want the keys now, but I feel that they are not 'playing ball' because they refuse to tell us who they have contacted in terms of banks, utilities, landlord and what they have done about the estate, plus they let us believe they were solicitors until they were found out.
Do they have to sell the flat and take the keys or can we sell the flat ourselves via an estate agent and then ask the executor to divide the proceeds equally between myself and my brother?