how can i use apps for uk without sacrificing my benefits in apple family subscription
You cannot. If you want to get UK apps you have to be signed into the UK store which you do by having your account set to the UK. However, all family sharing members have to have their accounts set to the same country so if you do change to the UK store you will have to leave the family sharing group.
Since you have moved to the UK, your account really should be signed into the UK. The support article Change your Apple Account country or region - Apple Support describes how to change your country setting on everything using your Apple Account, and the requirements and results of doing this.
Note that there are no easy workarounds to this. Your iPhone can only be signed into one Apple Account at a time, so trying to do something such as creating a second account for the UK isn't a solution.
Legal - Apple Media Services - Apple
"All Family members must share the same Home Country."