2) Do you still have to honour redundancy clauses (from their contract) in full e.g 3 month notice-period?

Currently employment legislation has not changed in recognition of the extenuating circumstances that Covid19 has put small businesses in, so yes, an employer has to honour redundancy clauses. Which can potentially be more expensive than keeping staff.
The best thing to do is take employees through the regular change process (see below) and try to jointly come up with alternatives such as LWOP (which allows them to be employed elsewhere until you’re in a position to get them back on board) or perhaps a temporary salary reduction (which they have to agree to but it may be more palatable than losing a job).
You can fast-track the below but remember to be reasonable. This shouldn’t for example all happen in one or two days:
Step 1 – Document your business case
Step 2 – Document your proposal
Step 3 – Present your proposal to employees
Step 4 – Gather feedback
Step 5 – Genuinely consider the feedback
Step 6 – Confirm the new structure – in writing and via a meeting or technology
Step 7 – Implement the change – and keep talking with your staff

At this time of uncertainty a lump sum of money would be reassuring to some staff, so be prepared for them wanting to take their entitlements (and it may be worth talking to the bank in advance of this process if that is an option for you)