MainViewModel.cs

using DevExpress.Mvvm;
using DevExpress.Mvvm.DataAnnotations;
using DevExpress.Mvvm.Xpf;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SynchronizeEditValuesInEditForm_MVVM {
    public class DataItem {
        public int Amount { get; set; }

        public int Price { get; set; }

        public int PositionValue { get => Price * Amount; }

        public bool CanEdit { get; set; } = true;

        public DataItem(Random random) {
            Amount = random.Next(1, 10);
            Price = random.Next(100, 1000);
        }
    }
    class MainViewModel : ViewModelBase {
        public ObservableCollection<DataItem> Items { get; }

        public MainViewModel() {
            Items = new ObservableCollection<DataItem>(GetData(10));
        }

        static IEnumerable<DataItem> GetData(int amount) {
            var random = new Random();
            return Enumerable.Range(0, amount).Select(i => new DataItem(random));
        }

        [Command]
        public void SynchronizeValues(CellValueChangedArgs args) {
            var editFormArgs = (CellValueChangedInEditFormArgs)args;
            if(editFormArgs == null) {
                return;
            }

            if(args.FieldName == nameof(DataItem.CanEdit)) {
                var priceData = editFormArgs.CellEditors.FirstOrDefault(x => x.FieldName == nameof(DataItem.Price));
                priceData.ReadOnly = !bool.Parse(args.Value.ToString());
                return;
            }

            if(args.FieldName == nameof(DataItem.Price)) {
                var positionValueData = editFormArgs.CellEditors.First(d => d.FieldName == nameof(DataItem.PositionValue));
                var amountData = editFormArgs.CellEditors.First(d => d.FieldName == nameof(DataItem.Amount));

                int price = 0;

                int.TryParse((string)args.Value, out price);
                positionValueData.Value = (int)amountData.Value * price;
            }
        }

        [Command]
        public void InitializeEditing(RowEditStartingArgs args) {
            var priceData = args.CellEditors.FirstOrDefault(x => x.FieldName == nameof(DataItem.Price));
            var canEditData = args.CellEditors.FirstOrDefault(x => x.FieldName == nameof(DataItem.CanEdit));
            priceData.ReadOnly = !(bool)canEditData.Value;
        }
    }
}