ISS Vanguard

Yes — other crewmembers may Assist by adding dice from their section to the acting crewmember's roll pool; Assist dice are added before rolling and are provided from the assisting crewmember's dice subject to Convert/ability limits (they are treated as part of the roll pool when resolving the check). (pp.16, 23, 32)

Spending a die pays an effect and that die stays spent until refreshed at Rest or round end, while Exertion lets you sacrifice a die (or take the Exhausted condition) to refresh your pool immediately; sacrificed/spent dice are returned only when rules specifically refresh them. (pp.20, 31)

Injury dice are placed by Injury cards and are included in Dice Checks as specified by the injury (often producing negative or special faces), while Danger dice are rolled when an action forces them (e.g., Travel) and can cause extra consequences or injuries; resolve their faces during Dice Check resolution and remove Injuries only by the card’s removal instructions or medical/clearance effects. (pp.22, 33, 40)

You get all icons shown on the die face — multi-icon dice produce every listed effect when that face is used/resolved, unless a specific effect says otherwise. (pp.33–34)

Travel is resolved by the acting crewmember spending the required die(s) or, if they don't spend, by resolving the Danger die (you cannot split the Travel cost between crewmembers); follow the Travel steps for path, icons, and any injury or Danger die effects. (pp.18, 30)