I'm not sure in the circumstances that it would be straightforward obtaining consent to sell either property. One has a relative who presumably lacks the ability to make informed decisions on his/her own behalf. Does this person have a trustee or a committee acting for them? The other has an elderly relative residiing there- is this the other tenant in common? Would either party WANT to sell?
I personally would agree with your solicitor that this is definitely an estate where you should take full legal and tax advice.
Revenue are usually very understandinig when it comes to situations like this and it is possible they might, if presented with a good case that you are not yet beneficially entitled to the properties given the circumstances, agree to defer any tax payable until the sale of one or death of one of the relatives etc.