Before you decide any technical solutions, do the business decision first. Are you willing to and/or capable of doing this ? For example, what percentage of revenue will come from these 2 customers overall and does it add up in the long term vision for your company ?

Lets say you decide to do it. Then make sure you are charging like 5-10x premium just to even entertain the idea. This is what you will call "Enterprise" and charge for EVERYTHING. Remember that if you deviate from your regular deployment etc, you will have to add extra work to support and maintain these additional things. So charge for those as well.

More importantly, if it doesn't align with your business vision, don't do it unless you are struggling to pay bills or interested in this space.

Source: I run a SAAS where we ended up doing mess like this and even though we charge more for that stuff, it has not added up for us in the overall direction/vision because we want to be a pure multi-tenant fast growing SAAS and don't have teams to handle too much enterprise yet.