This is not a problem! Altis will still work for you even if the other side of the transaction are not using it. When you create your transaction, you should select the other side as normal. They will receive an invitation to transact with you which they must respond to so that Altis knows if they are using it or not. If the other side are not using Altis, but fail to let the system know, the system will not allow you to amend certain elements of the system.
If the other side are not using Altis, they will receive notifications straight to their email address every time you update the transaction. They will receive the documents you upload as email attachments.