Under Tier 4 restrictions players may only use the courts for singles tennis unless all players are from the same household. The only exceptions are for junior coaching.
All other requirements re hygiene and track and trace etc remain.
A summary of the impact of the restrictions on outdoor tennis in the different tiers can be found at

https://www.lta.org.uk/globalassets/news/2020/local-restrictions-grid—tennis-activity-by-tier.pdf