Structural issues cracking

[Jasonsm19]

Any advice welcome please , awaiting SE survey. House has 2 storey extension to rear. Surveyor think undersized beam used and caused deflection but can’t be sure not ground level. Issues - vertical crack full length of house outside at the junction of extension and house inc through damp proof. Internal cracks same location downstairs and up. Further diagonal cracking in 2 places at rear thought to be from deflection - sloping of ceiling rear bedroom and bathroom. Awaiting SE but trying to understand how much potentially to allow for replacement beam and works If required and movement junction being installed at junction. Cheers